Polymer composite based thermal neutron detectors

ABSTRACT

Polymer composite neutron detector materials are described. The composite materials include an aromatic polymer matrix, such as an aromatic polyester. Distributed within the polymer matrix are neutron capture agents, such as  6 LiF nanoparticles, and organic or inorganic luminescent fluors. The composite materials can be formed into stretched or unstretched thin films, fibers or fiber mats.

RELATED APPLICATIONS

The presently disclosed subject matter is based on and claims thebenefit of U.S. Provisional Patent Application Ser. No. 61/624,009,filed Apr. 13, 2012; the disclosure of which is incorporated herein byreference in its entirety.

GOVERNMENT INTEREST

This invention was made with government support under Grant No.2009-DN-077-ARI031 awarded by the Domestic Nuclear Detection Office ofthe United States Department of Homeland Security and the NationalScience Foundation. The government has certain rights in the invention.

TECHNICAL FIELD

The presently disclosed subject matter relates to composite materialscomprising a neutron capture agent, an aromatic polymeric matrixmaterial, and an organic or inorganic luminescent fluor. The compositematerials can be used for thermal neutron detection. In someembodiments, the composite materials can be formed into nanofibers orthin films.

ABBREVIATIONS

-   -   μ=micron    -   %=percentage    -   ° C.=degrees Celsius    -   AIBN=azobisisobutyronitrile    -   AVP=aryl vinyl polymer    -   cc=cubic centimeter    -   CCD=charge-coupled device    -   cps=counts per second    -   DCM=dichloromethane    -   eq=equivalents    -   g=grams    -   HCl=hydrochloric acid    -   He=helium    -   Li=lithium    -   LiF=lithium fluoride    -   LLD=lower level discriminator    -   MeV=mega electron volt    -   mL=milliliter    -   mmol=millimole    -   M_(n)=number average molecular weight    -   nm=nanometer    -   PEN=polyethylene naphthalate    -   PHP=proton harvesting polymer    -   PMT=photomultiplier tube    -   POPOP=1,4-bis-(5-phenyloxazol-2-yl)    -   PPO=2,5-diphenyloxazole    -   PS=polystyrene    -   PSD=pulse shape discrimination    -   PTN=polytrimethylene naphthalate    -   P2VN=poly(2-vinylnaphthalene)    -   PVT=polyvinyl toluene    -   Sal=salicylate    -   SEM=scanning electron microscope    -   THF=tetrahydrofuran    -   TND=thermal neutron detector    -   UV=ultraviolet

BACKGROUND

Scintillators are materials that can emit light upon absorbing radiationor energy from ionizing radiation. The research, defense, and industrialcommunities use scintillators as radiation detectors in a variety ofapplications, such as, but not limited to, imaging, nuclear powergeneration, detection of special nuclear materials, and homelandsecurity.

Detectors for the detection of neutrons in the presence of photons canuse many different methods to discriminate signals that originate fromeither neutrons or photons. As an example, use of ³He in a pressurizedtube for neutron detection permits discrimination of neutrons fromphotons by pulse amplitude. These detectors fail to correctlydiscriminate neutrons from photons only about one per 50,000 events.There are a few other scintillation materials that have slightlydifferent light output characteristics when the energy is deposited by aphoton or by a charged particle. This permits pulse shape discrimination(PSD) with sophisticated electronics. Another approach is to employdetectors with a very small probability of interaction for photons and arelatively high probability of interaction for neutrons. Some detectorsof this type can achieve essentially 100% discrimination if chargedparticles are directly detected.

There is an ongoing need in the research, defense and industrialcommunities for scintillators that demonstrate improved capabilities interms of light output, detection efficiency, high count rate capability,better time resolution of events, and, for neutron scintillators, fewerfalse counts due to gamma radiation. Especially in view of the imminentshortage of ³He, there is a need for an inexpensive replacementtechnology for thermal neutron detection, particularly for replacementtechnologies that provide easy to make detectors that can have variousgeometries and/or sizes.

SUMMARY

In some embodiments, the presently disclosed subject matter provides apolymer composite comprising: a polymeric matrix material, wherein thematrix material comprises an organic polymer, copolymer or blendthereof, and wherein the matrix material comprises at least one polymeror copolymer comprising an aromatic moiety; a neutron capture agentdistributed within the matrix material, optionally wherein the neutroncapture agent comprises a ⁶Li compound; and an organic or inorganicluminescent fluor distributed within the matrix material.

In some embodiments, the matrix material comprises a polymer, copolymeror blend thereof comprising an aromatic moiety having a higher quantumyield than the quantum yield of phenyl. In some embodiments, the matrixmaterial comprises at least one aromatic moiety selected from the groupcomprising naphthylene, anthracene, fluorene, terphenyl, phenanthrene,pyridine, furan, and thiophene.

In some embodiments, the matrix material comprises a polymer orcopolymer selected from the group comprising a polyester, a polyamide, apolyether, a polyimide, a polythioester, a polyarylvinyl, avinylpolyether, a vinylpolyester, a vinylpolyamide, and avinylpolythioester. In some embodiments, the matrix material comprises apolyester. In some embodiments, the polyester is selected from the groupcomprising polyethylene naphthalate (PEN), polytrimethylene naphthalate(PTN), poly(9H-fluorene-9,9-dimethanol malonate),poly(9H-fluorene-9,9-dimethanol terephthalate), andpoly(4,4′-(9-fluorenylidene)-diphenol terephthalate).

In some embodiments, the matrix material comprises a derivatizedpolyacrylic or polyalkylacrylic acid, wherein acid groups of thepolyacrylic or polyalkylacrylic acid are derivatized to form ester,thioester or amide linked side chains, wherein the side chains comprisearomatic groups.

In some embodiments, the neutron capture agent is non-hygroscopic. Insome embodiments, the neutron capture agent comprises ⁶LiF micro- ornanoparticles. In some embodiments, the micro- or nanoparticles are 3.2microns or smaller. In some embodiments, the nanoparticles are about 200nm or smaller, and/or in some embodiments, about 100 nm or smaller.

In some embodiments, the organic or inorganic luminescent fluor isselected based on acceptor donor resonance and/or is selected from thegroup comprising 2,5-diphenyloxazole (PPO),1,4-bis-(5-phenyloxazol-2-yl) (POPOP), anthracene,9,9,9′,9′,9″,9″-hexakis(octyl)-2,7′,2′,7″-trifluorene, n-terphenyl,2-biphenyl-5-phenyl-1,3-oxazole, 2-biphenyl-5(α-naphthyl)-1,3-oxazole,2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole,2-(4′-tert-butylphenyl)-5-(4″-biphenylyl)-1,3,4-oxadiazole,n-bis-(o-methylstyryl)-benzene 1,4-di-(5-phenyl-2-oxazolyl)-benzene,conjugated polymeric and oligomeric dyes, metal organic framework dyes,quantum dots and two-photon absorber semiconductor fluors.

In some embodiments, the composite has a ratio of matrix material toneutron capture agent of between about 3:1 by weight and about 1:2 byweight. In some embodiments, the composite comprises about 5% or less byweight of the organic or inorganic luminescent fluor. In someembodiments, the composite comprises ⁶Li salicylate or ⁶LiF as a neutroncapture agent and poly(2-vinylnaphthalene) (P2VN) as a matrix material.In some embodiments, the composite comprises ⁶LiF as a neutron captureagent and PEN as a matrix material.

In some embodiments, the presently disclosed subject matter provides afilm comprising a polymer composite comprising: a polymeric matrixmaterial, wherein the matrix material comprises an organic polymer,copolymer or blend thereof, and wherein the matrix material comprises atleast one polymer or copolymer comprising an aromatic moiety; a neutroncapture agent distributed within the matrix material, wherein theneutron capture agent comprises a ⁶Li compound; and an organic orinorganic luminescent fluor distributed within the matrix material.

In some embodiments, the film has a thickness of about 500 microns orless. In some embodiments, the film has a thickness of about 220 micronsor less. In some embodiments, the film has a thickness of about 50microns or less. In some embodiments, the film is a biaxially oruniaxially stretched film. In some embodiments, the film is thermallyannealed. In some embodiments, the thermal annealing is performed at atemperature between about 150° C. and about 180° C.

In some embodiments, the matrix material comprises a polymer orcopolymer selected from the group comprising a polyester, a polyamide, apolyether, a polyimide, a polythioester, a vinylpolyether, avinylpolyester, a vinylpolyamide, and a vinylpolythioester. In someembodiments, the matrix material is a polyester. In some embodiments,the polyester is selected from the group comprising polyethylenenaphthalate (PEN), polytrimethylene naphthalate (PTN),poly(9H-fluorene-9,9-dimethanol malonate),poly(9H-fluorene-9,9-dimethanol terephthalate), andpoly(4,4′-(9-fluorenylidene)-diphenol terephthalate).

In some embodiments, the neutron capture agent is non-hygroscopic. Insome embodiments, the neutron capture agent comprises ⁶LiF micro- ornanoparticles. In some embodiments, the matrix material comprises PEN,the neutron capture agent comprises ⁶LiF micro- or nanoparticles and thefilm is a stretched and/or thermally annealed film.

In some embodiments, the film comprises a polymer composite having aratio of matrix material to neutron capture agent of between about 3:1and about 1:5 by weight. In some embodiments, the film comprises apolymer composite comprising about 49.5% by weight PEN, about 49.5% byweight ⁶LiF, and about 1% by weight9,9,9′,9′,9″,9″-hexakis(octyl)-2,7′,2′,7″-trifluorene. In someembodiments, the film comprises a polymer composite comprising about 70%by weight PEN, about 25% by weight ⁶LiF, and about 5% by weightPPO/POPOP.

In some embodiments, the film has a neutron count rate per mg of ⁶Li ofbetween about 4 and about 12 counts per second (cps).

In some embodiments, the film is prepared by: providing a mixture of thematrix material, a neutron capture agent, and a luminescent fluor; andhot pressing or extruding the mixture to form the film. In someembodiments, providing the mixture comprises preparing micro- ornanoparticles of ⁶LiF; and mixing the micro- or nanoparticles with thematrix material and the luminescent fluor.

In some embodiments, the presently disclosed subject matter provides anapparatus for detecting neutron radiation, wherein the apparatuscomprises a photon detector and a polymer composite comprising: apolymeric matrix material, wherein the matrix material comprises anorganic polymer, copolymer or blend thereof, and wherein the matrixmaterial comprises at least one polymer or copolymer comprising anaromatic moiety; a neutron capture agent distributed within the matrixmaterial, wherein the neutron capture agent comprises a ⁶Li compound;and an organic or inorganic luminescent fluor distributed within thematrix material. In some embodiments, the polymer composite is in theform of a film having a thickness of about 500 microns or less.

In some embodiments, the presently disclosed subject matter provides amethod for detecting neutron radiation, wherein the method comprises:providing a polymer composite comprising a polymeric matrix material,wherein the matrix material comprises an organic polymer, copolymer orblend thereof, and wherein the matrix material comprises at least onepolymer or copolymer comprising an aromatic moiety; a neutron captureagent distributed within the matrix material, wherein the neutroncapture agent comprises a ⁶Li compound; and an organic or inorganicluminescent fluor distributed within the matrix material; disposing thepolymer composite in the path of a beam of radiation, wherein the matrixand the luminescent fluor of the polymer composite emits light when thecomposite absorbs said radiation; and detecting neutron radiation bydetecting the light emitted by the composite, wherein the detectingdiscriminates between neutron and gamma radiation.

In some embodiments, providing a polymer composite of claim 1 comprisesproviding a film of the polymer composite. In some embodiments,providing the film comprises providing a biaxially or uniaxiallystretched and/or thermally annealed film.

In some embodiments, the presently disclosed subject matter provides amethod of making a film or molded coupon comprising a polymer compositecomprising a polymeric matrix material, wherein the matrix materialcomprises an organic polymer, copolymer or blend thereof, and whereinthe matrix material comprises at least one polymer or copolymercomprising an aromatic moiety; a neutron capture agent distributedwithin the matrix material, wherein the neutron capture agent comprisesa ⁶Li compound; and an organic or inorganic luminescent fluordistributed within the matrix material, wherein the method comprises:providing micro- or nanoparticles of the neutron capture agent; mixingthe micro- or nanoparticles with the matrix material and the luminescentfluor to form a mixture; and pressing and heating the mixture to formthe film or molded coupon.

In some embodiments, the matrix material is powdered prior to mixingwith the micro- or nanoparticles and the luminescent fluor. In someembodiments, the mixture is ground into a powder and the powder issieved and/or blended to obtain a homogenous mixture. In someembodiments, the mixture is sieved through a 500 μm or smaller sieve.

In some embodiments, the neutron capture agent is ⁶LiF micro- ornanoparticles that are 3.2 microns or smaller. In some embodiments,providing the neutron capture agent comprises titrating ⁶Li enrichedlithium hydroxide with hydrofluoric acid to provide precipitated ⁶LiFparticles, and collecting the precipitated particles. In someembodiments, the neutron capture agent is ⁶LiF nanoparticles that areabout 200 nm or about 100 nm or smaller. In some embodiments, the ⁶LiFnanoparticles are provided by ball milling (e.g., cryo ball milling)larger particles.

In some embodiments, pressing and heating the mixture comprises heatingthe mixture to a temperature of about 260° C. to about 300° C. In someembodiments, the method of making a film or molded coupon furthercomprises stretching the film. In some embodiments, the stretching isperformed at a temperature of between about 120° C. and about 150° C. Insome embodiments, the stretching is biaxial or uniaxial stretching. Insome embodiments, the method further comprises thermally annealing thefilm. In some embodiments, the annealing is performed at a temperaturebetween about 150° C. and about 180° C.

In some embodiments, the presently disclosed subject matter provides amethod of making a polymer composite comprising a polymeric matrixmaterial, a neutron capture agent and an organic or inorganicluminescent fluor, wherein the method comprises solution casting asolution comprising the matrix material, the neutron capture agent, andthe luminescent fluor. In some embodiments, the solution comprisestetrahydrofuran as a solvent.

In some embodiments, the presently disclosed subject matter provides afiber comprising a polymer composite comprising: a polymeric matrixmaterial, wherein the matrix material comprises an organic polymer,copolymer or blend thereof, and wherein the matrix material comprises atleast one polymer or copolymer comprising an aromatic moiety; a neutroncapture agent distributed within the matrix material, wherein theneutron capture agent comprises a ⁶Li compound; and an organic orinorganic luminescent fluor distributed within the matrix material.

In some embodiments, the fiber is prepared by electrospinning,extrusion, meltblowing, and/or meltdrawing. In some embodiments, thefiber has an average diameter between about 200 nm and about 500microns. In some embodiments, the fiber is prepared from a polymercomposite comprising ⁶Li salicylate or ⁶LiF as the neutron capture agentand polystyrene (PS) or a blend of poly(2-vinylnapthalene) (P2VN) andpolystyrene (PS) as the matrix material. In some embodiments, thepresently disclosed subject matter provides a fiber mat comprising thefiber comprising the polymer composite.

Accordingly, it is an object of the presently disclosed subject matterto provide polymer composites (including films, fibers and fiber matsthereof) and to fabricate detectors comprising the composites thatefficiently detect thermal neutrons and that can discriminate neutronfrom gamma radiation.

An object of the presently disclosed subject matter having been statedhereinabove, and which is achieved in whole or in part by the presentlydisclosed subject matter, other objects will become evident as thedescription proceeds hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 shows emission spectra of unstretched pure polyethylenenaphthalate (PEN) film, stretched pure PEN film, and stretechedcomposite PEN film.

FIG. 2 shows excitation spectra of unstretched pure polyethylenenaphthalate (PEN) film, stretched pure PEN film, and stretechedcomposite PEN film.

FIG. 3 shows neutron count rate spectra for an unstretched compositepolyethylene naphthalate (PEN) film and a stretched composite PEN film.The composite films have a PEN matrix with 50 weight % ⁶LiF and 1 weight% of a fluor. For comparison, the spectra of a commercial lithiatedglass scintillator (GS20) which is 2 mm (i.e., 2,000 microns) thick isalso shown.

FIG. 4A shows neutron and gamma discrimination curves for theunstretched composite polyethylene naphthalate (PEN) film described inFIG. 3.

FIG. 4B shows neutron and gamma discrimination curves for the stretchedcomposite polyethylene naphthalate (PEN) film described in FIG. 3.

FIG. 5A shows pulse height spectra obtained by exposure to alphaparticle radiation for a commercial lithiated glass scintillator (GS20;open circles), a 31 micron thick stretched pure polyethylene naphthalate(PEN) film (open squares), a 75 micron thick stretched composite PENfilm (containing 50 weight % ⁶LiF and 1 weight % fluor; open triangles),and a 223 micron thick unstretched composite PEN film (containing 50weight % ⁶LiF and 1 weight fluor; filled diamonds).

FIG. 5B shows pulse height spectra obtained by exposure to beta particleradiation for a commercial lithiated glass scintillator (GS20), a 31micron thick stretched pure polyethylene naphthalate (PEN) film, a 75micron thick stretched composite PEN film (containing 50 weight % ⁶LiFand 1 weight % fluor), and a 223 micron thick unstretched composite PENfilm (containing 50 weight % ⁶LiF and 1 weight % fluor).

FIG. 5C shows the pulse height spectra obtained by exposure to gammaparticle radiation for a commercial lithiated glass scintillator (GS20),a 31 micron thick stretched pure polyethylene naphthalate (PEN) film, a75 micron thick stretched composite PEN film (containing 50 weight %⁶LiF and 1 weight % fluor), and a 223 micron thick unstretched compositePEN film (containing 50 weight % ⁶LiF and 1 weight % fluor).

FIG. 6 is a schematic drawing of an apparatus for detecting neutronradiation according to the presently disclosed subject matter. Apparatus10 includes photon detector 12 optically coupled to polymer composite14. Apparatus 10 can optionally include electronics 16 for recordingand/or displaying electronic signal from photon detector 12. Thus,optional electronics 16 can be in electronic communication with photondetector 12.

FIG. 7 is a graph showing gamma count rate (red) and net neutron countrate (green) spectra for composite films comprising 70 weightpolyethylene naphthalate (PEN), 25 weight % ⁶LiF, and 5 weight % fluor(a mixture of 2,5-diphenyloxazole (PPO) and1,4-bis-(5-phenyloxazol-2-yl) (POPOP)). Curves are shown for both anunstretched cast composite film (Cast composite PEN Film; total mass44.2 milligrams (mg), 340 microns (μm) thick) and a thermally annealedcast composite film (Post processed composite PEN film, total mass 44.2mg, 340 μm thick). The gamma count was measured using response to cobalt60 (⁶⁰Co) and the net neutron count rate was measured using response tocalifornium 252 (²⁵²Cf). For comparison, the spectra of a commerciallithiated glass scintillator (GS20) which is 2.1 millimeters (mm) thick(i.e., 2,100 microns thick; total mass 2.47 grams (g)) are also shown.

FIG. 8 is a graph showing gamma count rate (red) and net neutron countrate (green) spectra for composite films comprising 70 weightpolyethylene naphthalate (PEN), 25 weight % ⁶LiF, and 5 weight % fluor(a mixture of 2,5-diphenyloxazole (PPO) and1,4-bis-(5-phenyloxazol-2-yl) (POPOP)). Curves are shown for both anunstretched cast composite film (Cast composite PEN Film; total mass1.02 grams (g), 490 microns (μm) thick) and a thermally annealed castcomposite film (Post processed composite PEN film, total mass 1.02 g,490 μm thick). The gamma count was measured using response to cobalt 60(⁶⁰Co) and the net neutron count rate was measured using response tocalifornium 252 (²⁵²Cf). For comparison, the spectra of a commerciallithiated glass scintillator (GS20) which is 2.1 millimeters (mm) thick(i.e., 2,100 microns thick; total mass 2.47 grams (g)) are also shown.

DETAILED DESCRIPTION

Particularly in view of projected shortages of ³He, there is a need foran inexpensive replacement technology for thermal neutron detection. Thechallenges in the development of new detectors include discriminatingneutrons from background noise and other radiation like gamma and beta,getting high count rates, and increasing efficiency, light output, andresolution in neutron detection. Many Li-based detectors currentlyavailable are based on ceramic glasses that are difficult to fabricatein large size. Further, existing detector materials can be structurallyrigid and expensive to fabricate.

The presently disclosed subject matter relates, in some aspects, to thinfilm, fiber, or fiber mat detectors for detecting thermal and epithermalneutrons in the presence of gamma radiation, and to methods of preparingthe solid thin film detectors. These detectors can be based on aromaticpolymer composites that include neutron capture agents. In someembodiments, the presently disclosed subject matter provides compositescomprising: a polymeric matrix material comprising an organic group witha higher quantum yield than phenyl (such as, but not limited to,naphthalene, anthracene, fluorene, terphenyl, phenanthrene, pyridine,furan, and thiophene); a neutron capture agent comprising a ⁶Li compounddistributed within the matrix material; and an organic or inorganicluminescent fluor (e.g., a luminescent activator or a wavelengthshifter) distributed within the matrix material. The matrix and/orluminescent fluors can emit photons which can be counted by aphotomultiplier tube (PMT) or a charge-coupled device (CCD) camera (or aphotodiode, etc.), and signal thus obtained can be calibrated to theneutron count. In some embodiments, the presently disclosed subjectmatter provides ⁶LiF-based scintillator polymer composites.

In some embodiments, the presently disclosed subject matter provides amethod for creating novel scintillator detectors for neutrons which arecapable of discrimination of neutrons against gamma radiation. Thepresently disclosed detectors can also exhibit a high intrinsicefficiency for counting neutrons.

Some of the advantages of the presently disclosed neutron detectorsinclude: (1) ease of synthesis and production, (2) economy ofproduction, (3) intrinsic neutron to gamma discrimination, (4) highefficiency of neutron detection, (5) ease of making large volume, largearea detectors in various flexible geometries, and (6) ease ofimplementation in public places.

The presently disclosed subject matter will now be described more fully.The presently disclosed subject matter can, however, be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein below and in the accompanying Examples.Rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the scope of theembodiments to those skilled in the art.

All references listed herein, including but not limited to all patents,patent applications and publications thereof, and scientific journalarticles, are incorporated herein by reference in their entireties tothe extent that they supplement, explain, provide a background for, orteach methodology, techniques, and/or compositions employed herein.

I. Definitions

While the following terms are believed to be well understood by one ofordinary skill in the art, the following definitions are set forth tofacilitate explanation of the presently disclosed subject matter.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which the presently disclosed subject matter belongs.

Following long-standing patent law convention, the terms “a”, “an”, and“the” refer to “one or more” when used in this application, includingthe claims.

The term “and/or” when used in describing two or more items orconditions, refers to situations where all named items or conditions arepresent or applicable, or to situations wherein only one (or less thanall) of the items or conditions is present or applicable.

The use of the term “or” in the claims is used to mean “and/or” unlessexplicitly indicated to refer to alternatives only or the alternativesare mutually exclusive, although the disclosure supports a definitionthat refers to only alternatives and “and/or.” As used herein “another”can mean at least a second or more.

The term “comprising”, which is synonymous with “including,”“containing,” or “characterized by” is inclusive or open-ended and doesnot exclude additional, unrecited elements or method steps. “Comprising”is a term of art used in claim language which means that the namedelements are essential, but other elements can be added and still form aconstruct within the scope of the claim.

As used herein, the phrase “consisting of” excludes any element, step,or ingredient not specified in the claim. When the phrase “consists of”appears in a clause of the body of a claim, rather than immediatelyfollowing the preamble, it limits only the element set forth in thatclause; other elements are not excluded from the claim as a whole.

As used herein, the phrase “consisting essentially of” limits the scopeof a claim to the specified materials or steps, plus those that do notmaterially affect the basic and novel characteristic(s) of the claimedsubject matter.

With respect to the terms “comprising”, “consisting of”, and “consistingessentially of”, where one of these three terms is used herein, thepresently disclosed and claimed subject matter can include the use ofeither of the other two terms.

Unless otherwise indicated, all numbers expressing quantities of time,temperature, neutron count rate, thickness, diameter, weight percentage(%), and so forth used in the specification and claims are to beunderstood as being modified in all instances by the term “about”.Accordingly, unless indicated to the contrary, the numerical parametersset forth in this specification and attached claims are approximationsthat can vary depending upon the desired properties sought to beobtained by the presently disclosed subject matter.

As used herein, the term “about”, when referring to a value is meant toencompass variations of in one example ±20% or ±10%, in another example±5%, in another example ±1%, and in still another example ±0.1% from thespecified amount, as such variations are appropriate to perform thedisclosed methods.

As used herein the terms “microparticle” and “nanoparticle” have themeaning that would be ascribed to them by one of ordinary skill in theart. In some embodiments, “microparticle” can refer to a particle havinga dimension (e.g., a width or diameter) ranging from about 1000 micronsdown to about 0.1 microns. In some embodiments, the microparticle has adimension ranging from about 100 microns to about 1 micron. In someembodiments, “nanoparticle” refers to a particle having a dimensionranging from about 1 micron to about 0.1 nm. In some embodiments, thenanoparticle has a dimension ranging from about 500 nm to about 1 nm. Insome embodiments, the nanoparticle has a dimension that is smaller thanabout 200 nm, such as but not limited to about 100 nm. Micro- andnanoparticles can be any shape, e.g., cubic, spherical, or irregularlyshaped.

As used herein, a “polymerizable monomer” refers to a molecule that canundergo polymerization, thereby contributing constitutional units, i.e.,a repeating atom or group of atoms, to the essential structure of apolymer macromolecule.

As used herein, a “polymer” refers to a molecule which comprises themultiple repetition of units derived from molecules of low relativemolecular mass, e.g., polymerizable monomers and/or oligomers.

An “oligomer” refers to a molecule of intermediate relative molecularmass, the structure of which comprises a small plurality (e.g., 2-100,2-50, 2-20, or 2-10) of units derived from molecules of lower relativemolecular mass.

A “copolymer” refers to a polymer derived from more than one species ofpolymerizable monomer. Copolymers include block copolymers (containingchains of oligomers or polymers where each chain is an oligomeric orpolymeric chain based on a different monomeric unit), random copolymers,where monomeric units from different monomers are randomly ordered inthe copolymer, and statistical copolymers, where there is a statisticaldistribution of monomeric units from the different monomers in thecopolymer chain.

A polymer blend refers to a mixture to two different types of alreadyformed polymer or copolymer.

A “chain” refers to the whole or part of a polymer or an oligomercomprising a linear or branched sequence of constitutional units betweentwo boundary constitutional units, wherein the two boundaryconstitutional units can comprise an end group, a branch point, orcombinations thereof. A “main chain” or “backbone” refers to a chainfrom which all other chains are regarded as being pendant. A “sidechain” refers to a smaller chain attached to the main chain. In someembodiments, a side chain can contain a single, non-repeatingconstitutional unit.

The terms “aryl” and “aromatic” refer to groups that can have a singlearomatic ring, or multiple aromatic rings that are fused together,linked covalently, or linked to a common group, such as, but not limitedto, a methylene or ethylene moiety. The term aryl can refer to bothnon-heterocyclic aryl groups and aryl groups wherein one or more of thecarbon atom of an aromatic ring backbone has been replaced by aheteroatom. Thus, the term aryl includes heteroaryl groups, including,but not limited to, furan, thiophene, pyridine, pyrimidine, pyridazine,pyrazine, imidazole, benzimidazole, benzofuran, and triazole (e.g.,1,2,4-triazole and 1,2,3-triazole).

In some embodiments, the term aryl specifically refers to anon-heterocyclic aromatic group comprising between 6 and 26 carbon atomsin the ring structure or structures making up the aryl group backbone(i.e., the aromatic ring structure or structures excluding any arylgroup substituents, as defined hereinbelow). For example, the aryl groupcan include monovalent radicals of benzene, biphenyl, naphthalene,anthracene, phenanthrene, chrysene, pyrene, tetracene,benzo[a]anthracene, dibenzo[a,j]anthracene, dibenzo[a,h]anthracene,dibenzo[a,c]anthracene, coronene, fluoranthene, benzo[a]pyrene,benzo[c]phenanthrene, benzo[b]fluoranthene], hexahelicine, and the like.In some embodiments, the aryl group is other than phenyl oralkyl-substituted phenyl.

The aryl group can be optionally substituted (a “substituted aryl”) withone or more aryl group substituents, which can be the same or different,wherein “aryl group substituent” includes alkyl, substituted alkyl,aryl, substituted aryl, aralkyl, hydroxyl, alkoxyl, aryloxyl,aralkyloxyl, carboxyl, acyl, halo, nitro, alkoxycarbonyl,aryloxycarbonyl, aralkoxycarbonyl, acyloxyl, acylamino, aroylamino,carbamoyl, alkylcarbamoyl, dialkylcarbamoyl, arylthio, alkylthio,alkylene, and —NR′R″, wherein R′ and R″ can each be independentlyhydrogen, alkyl, substituted alkyl, aryl, substituted aryl, and aralkyl.

Thus, as used herein, the term “substituted aryl” includes aryl groups,as defined herein, in which one or more atoms or functional groups ofthe aryl group are replaced with another atom or functional group,including for example, alkyl, substituted alkyl, halogen, aryl,substituted aryl, alkoxyl, hydroxyl, nitro, amino, alkylamino,dialkylamino, sulfate, and mercapto.

The term “heteroaryl” refers to any aryl group as defined hereinabove,wherein one or more carbon atoms of the aryl group ring backbone orbackbones is replaced by a heteroatom. The heteroatom can be N, S, O,Si, or B. Typical nitrogen-containing heteroaryl groups include, but arenot limited to, pyridinyl, triazolyl, imidazolyl, pyrimidinyl,pyridazinyl, triazinyl, indolyl, quinolinyl, and the like.

The term “arylene” refers to a bivalent aromatic hydrocarbon group.Exemplary arylene groups include, but are not limited to, phenylene,napthalene, biphenylene (i.e., —C₆H₄—C₆H₄—), and the like.

“Aralkyl” refers to an aryl-alkyl- group wherein aryl and alkyl are aspreviously described, and included substituted aryl and substitutedalkyl. Exemplary aralkyl groups include benzyl, phenylethyl, andnaphthylmethyl.

The terms “carboxy” and “carboxyl” refer to carboylic acid andcarboxylate groups and to their alkyl, aryl, aralkyl, andnitrogen-containing derivatives.

The terms “carboxylic acid” or “acid” can refer to the —C(═O)OH group.The term “carboxylate” refers to the deprotonated anion of a carboxylicacid (i.e., —C(═O)O⁻). Acid and/or carboxylate groups can be“derivatized” by forming covalent bonds upon reaction with an alcohol,amine, thiol or other nucleophilic compound.

The term “ester” refers to a compound including the group —C(═O)—O—R,wherein R is alkyl, aralkyl, or aryl. Polyesters can include —C(═O)—O—linkages in a polymer chain. Thus, the term “polyester” can refer to apolymer comprising ester linkages in the polymer main chain.

The term “thioester” refers to a compound including the group—C(═O)—S—R, wherein R is alkyl, aralkyl, or aryl. Polythioesters caninclude —C(═O)—S— linkages in a polymer chain.

The term “amide” refers to a compound including the group —C(═O)—NR′—R,wherein R and R′ are each H, alkyl, aralkyl, or aryl. Polyamides caninclude —C(═O)—NR′— linkages in a polymer chain.

The term “ether” refers to a compound including the group —R—O—R—,wherein each R is alkylene or arylene.

The term “imide” refers to a compound including the group—C(═O)—NR′—C(═O)—R, wherein R and R′ are each H, alkyl, aralkyl, oraryl. Polyimides are polymers of imide monomers. In some embodiments,polyimides can be prepared by reacting a diamine or a diisocyanide witha dianhydride.

The terms “polyarylvinyl” and “aryl vinyl polymer” refer to a polymerprepared from monomers comprising vinyl groups and aryl groups.Exemplary polyarylvinyl polymers include, but are not limited to,polystyrene and polyvinyltoluene.

The terms “vinylpolyester”, “vinylpolyamide”, “vinylpolythioester,” and“vinylpolyether” refer to polymers of vinyl (i.e., alkene-containing)monomers having ester, amide, thioester, or ether side chains. In someembodiments, these polymers are derivatized polyacrylic acid orpolyalkylacrylic acids wherein the acids groups are derivatized to formesters, thioester, or amides with aromatic group-containing alcohols,thiols or amines.

II. General Considerations

Neutron scintillators can employ stable isotopes with a high neutroncross section. In some embodiments, the presently disclosed subjectmatter provides composite materials comprising ⁶Li compounds as neutroncapture agents distributed within a polymer matrix scintillator. Onthermal neutron capture, the ⁶Li nucleus can undergo fission to producecharged particles with high kinetic energy (about 4.78 MeV), namely analpha particle (about 2.05 MeV) and a triton particle (about 2.73 MeV).These high-energy charged particles can leave behind them a field ofionization along their path length as they fragment the polymeric chainsof the matrix by breaking covalent bonds. These ionizations can in turncreate secondary electrons, secondary ions, and excitations in thearomatic matrix of the scintillator polymer of the presently disclosedcomposites, all of which can directly or indirectly take part inactivation of the polymer to produce excitations. Such excitations caneither produce photons directly through monomer/excimer emission(characterized by quantum yield), be dissipated by vibrational means, orbe transported through the matrix by random hopping to be eventuallyharvested by antenna molecules distributed within the matrix (e.g.,energy harvesting fluors, such as inorganic or organic luminescentfluors) that can concomitantly emit photons at a longer wavelength thanthe matrix. The transfer of energy to the lower energy excited state ofthe luminescent fluor can allow for re-radiation at a wavelength wherethe bulk material is more transparent, such that higher quantumefficiency is achieved. Thus, according to the presently disclosedsubject matter, the polymer matrix is more than simply a binder orstructural element, it also produces and transports excitationsefficiently.

II.A. Composites

Thus, in some embodiments, the presently disclosed subject matterprovides a polymer composite comprising a polymeric matrix material.Distributed within the polymeric matrix material (e.g., non-covalentlyencapsulated or embedded within the polymeric matrix material) can be aneutron capture agent and an organic or inorganic luminescent fluor. Thepolymeric matrix material can comprise an organic polymer, copolymer orblend thereof having high energy transport efficiency and comprising atleast one polymer or copolymer comprising an aromatic moiety.

Any suitable ratio of polymeric matrix material to neutron capture agentto fluor can be used. In some embodiments, the composite has a ratio ofmatrix material to neutron capture agent of between about 9:1 by weightto about 1:5 by weight (e.g., about 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1,2:1, 1.5:1, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5). Insome embodiments, the ratio of matrix material to neutron capture agentis between about 3:1 to about 1:5. In some embodiments, the ratio ofmatrix material to neutron capture agent is between about 3:1 and about1:2 by weight. In some embodiments, the ratio of matrix material toneutron capture agent is between about 1:1 and about 1:5 by weight. Insome embodiments, the ratio is between about 3:1 and about 1:1 byweight.

Typically, the amount of organic and/or inorganic luminescent fluor isrelatively low compared to the amount of matrix material and neutroncapture agent. In some embodiments, the composite comprises about 5%(e.g., about 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1, or 0.5%) or less byweight of the organic or inorganic luminescent fluor. In someembodiments, the composite comprises about 1% by weight of the organicor inorganic luminescent fluor.

II.A.i. Matrix Materials

In some embodiments, the polymer matrix is selected from the groupincluding, but not limited to, aromatic polyesters, polyamides,polyethers, polyimides, polythioesters, arylvinyl polymers (i.e.,“polyarylvinyls”, such as, but not limited to poly(anthrylenevinylene)(PAV) and poly(naphthalenevinylene) (PNV)), vinylpolyesters,vinylpolyethers, vinylpolyamides and polythioesters. In someembodiments, the polymer matrix is not polystyrene, polyvinyltoluene, orpoly(phenylenevinylene). In some embodiments, the polymer matrixincludes an aromatic moiety other than phenyl or alkyl-substitutedphenyl (e.g., methylphenyl). In some embodiments, the polymer matrix isstereo-regular. In some embodiments, the polymer matrix includes anaromatic moiety that has a higher energy transport efficiency and/orquantum yield than phenyl (i.e., a higher quantum yield than about 0.07)or methyl-substituted phenyl (i.e., a higher quantum yield than about0.17). In some embodiments, the aromatic moiety of the polymer isselected from the group including, but not limited to, naphthalene,anthracene, fluorine, terphenyl, phenanthrene, pyridine, furan, andthiophene. In some embodiments, the aromatic moieties are unsubstituted(i.e., with the exception of any bonding required to attach the aromaticmoiety to the backbone of the polymeric matrix). In some embodiments,the aromatic moiety can be substituted by one or more aryl groupsubstituents.

In some embodiments, the polymer matrix is an aromatic polyester. Insome embodiments, the matrix material comprises or consists ofpolyethylene naphthalate (PEN) or polytrimethylene naphthalate (PTN) ora blend or copolymer of both. In some embodiments PEN and PTN can bemodified by various functional groups (i.e., by one or more aryl groupsubstituents).

Polyesters in general have good structural integrity and their synthesisis relatively straight forward. A large variety of polymers can beprepared by several different routes. Aromatic polyesters are oftenhighly crystalline with high melting points and low solubility.Crystallinity can be decreased by introducing bulky side-groups (e.g.,alkyl or aryl groups) or kinks in the polymer backbone to make moresoluble polyesters.

Suitable polyesters can be prepared, for example, by reacting adicarboxylic acid or diacid chloride with a diol in a step-growthcondensation reaction, liberating water or HCl. Equimolar amounts ofreactants can be used to achieve high molecular weights. In someembodiments, the dicarboxylic acid can be malonic acid and the diacidchloride can be terephthaloyl chloride. A mixture of isophthaloylchloride and terephthaloyl chloride can be used to introduce kinks intothe polymer backbone. The diol generally can contain a scintillatingfunctional group (e.g., an aromatic moiety), such as fluorene, oranother aromatic group that has a high quantum yield.

The reaction between a dicarboxylic acid and a diol can be done in amelt, and liberated water can be removed in order to force the reaction.A catalyst such as zinc acetate or antimony trioxide can be used toobtain high molecular weights in a timely fashion. The reaction betweena diacid chloride and a diol can occur quickly and irreversibly at roomtemperature. A tertiary amine such as pyridine or triethylamine can beadded to neutralize the produced HCl, resulting in the hydrochloridesalt of the amine. Reactions can also be done in solution. Suitablesolvents include, but are not limited to, tetrahydrofuran (THF) ordichloromethane (DCM) and other ethers, halogenated alkanes, or aromaticsolvents. The reaction mixture can be heated in order to speed up thekinetics of the reaction, which should cause an increase in themolecular weight of the obtained polymer.

The structures of some exemplary polyester matrix polymers are shown inScheme 1, below. These exemplary polyesters includepoly(9H-fluorene-9,9-dimethanol malonate), which can be synthesized inthe melt, is soluble in a variety of solvents, melts at about 140° C.,and which turns yellow-brown in color upon melting due to decompositionof fluorine dimethanol. Poly(9H-fluorene-9,9-dimethanol terephthalate)can be synthesized by a diacid chloride route and is white in color.Poly(4,4′-(9-fluorenylidene)-diphenol terephthalate) can be synthesizedby an acid chloride route, is white in color, fairly soluble in avariety of solvents and give a good fluorescence spectrum. To introducekinks into the backbone in attempts to increase solubility mixtures ofacid chlorides (e.g., 50/50 and 70/30 mixtures of terephthaloylchloride/isophthaloyl chloride), for example, can be used.

In some embodiments, the matrix material can comprise a vinyl polymerwith ester (or amide, ether, or thioester)-linked scintillatingside-groups. The backbone of these vinylpolyester, vinylpolyamide,vinylpolyether, and vinylpolythioester polymers can be derived frommethacryloyl chloride (or another suitable vinyl-containing acidchloride). The acid groups of a polyacrylic acid or poly(alkylacrylicacid) polymer can react with thiols or alcohols to form thioester orester linked side chains or with amines to form amide linked sidechains. The side chains can be derived from, for example, the followinghigh quantum yield molecules: 9-anthracenemethanol, 9-fluorenemethanol,and 1,1′,4′,1″-terphenyl-4-thiol. Scheme 2 shows the structures of someexemplary vinylpolyesters and vinylpolythioesters.

II.A.ii. Neutron Capture Agent

Neutron scintillators can benefit from the presence of stable isotopeswith a high neutron cross section. Typically, the neutron capture agentof the presently disclosed materials comprises a ⁶Li compound. However,in some embodiments, other neutron capture agents, such as thoseincluding isotopes of boron (e.g., ¹⁰B), xenon (Xe), Cadmium (Cd),hafnium (Hf), Gadolinium (Gd), Cobalt (Co), Europium (Eu), and Ytterbium(Yb) can be used. When the neutron capture agent comprises ⁶Li, suitable⁶Li compounds can include, but are not limited to, ⁶Li-containing LiBH₄,LiOH, LiF, Li₂CO₂, LiCl, LiBF₄, LiClO₄, and Li salicylate (i.e., LiSal).

In some embodiments, the neutron capture agent is non-hygroscopic(and/or not reactive with water) or only slightly hygroscopic. Bynon-hygroscopic is meant a compound that does not absorb water or thatdoes not appreciably absorb water. In some embodiments, anon-hygroscopic compound is a compound that absorbs less than 5%weight/weight of water when exposed to ambient atmospheric conditionsfor 24 hours or longer (e.g., 1 week or more). In some embodiments, thenon-hygroscopic compound is a compound that absorbs less than 0.5%weight/weight of water when exposed to ambient atmospheric conditionsfor 24 hours or longer (e.g., 10 weeks) with high relative humidity(e.g., 80% relative humidity or higher). In some embodiments, theneutron capture agent is slightly hygroscopic, i.e., the agent canabsorb more water than a non-hygroscopic compound, but not enough waterto cause a composite material containing said agent to becomemechanically unstable or to degrade its performance (e.g., as ascintillator). Thus, in some embodiments, the ⁶Li compound isnon-hygroscopic, and is a compound such as, but not limited to,⁶Li-containing LiF or Li₂CO₃. In some embodiments, the ⁶Li compound isslightly hygroscopic, such as, but not limited to, ⁶Li-containing LiClO₄or LiSal. The non- or low hygroscopic nature of the ⁶Li compound can aidin the provision of composites and composite films that remainmechanically stable over time. Although ⁶LiSal can absorb moisture, itdoes not form unstable films when composites are made using arylvinylpolymers (e.g., P2VN).

In some embodiments, the ⁶Li compound is ⁶LiF. ⁶LiF is one of the fewlithium compounds that is thermally stable, non-hygroscopic, and thatdoes not violently react with water. ⁶LiF demonstrates one of thehighest transparencies in the UV and near blue region of the visiblespectra. Furthermore ⁶LiF has a very high density of 2.64 g/cc and has ahigh stoichiometric lithium content of 24%.

Generally, ⁶LiF has relatively low solubility in common organic solventsthat dissolve polymers. Thus, in some embodiments, it can beadvantageous to employ a ⁶Li compound that is soluble (e.g., ⁶LiSal) andforms a single phase or a nano-phase distribution within a scintillationpolymer matrix. However, an alternative to a single phase system is toobtain uniformly distributed ⁶LiF phases with a minimum possible meancrystal size with low standard deviation which in turn reducesself-absorption of charged particles within ⁶LiF crystals, increases theprobability of neutron interaction, and can improve transparency of thecomposite. ⁶LiF is also slightly soluble in THF (approximately 6 mg/mL),which can make it possible to process as a partially soluble componentin a polymeric composite with uniformity in composition.

In some embodiments, the neutron capture agent comprises ⁶LiF micro- ornanoparticles. The ⁶LiF micro- or nanoparticles can be prepared bytitrating lithium hydroxide with hydrofluoric acid. In some embodiments,the micro- or nanoparticles are about 100 microns or smaller (e.g.,about 100, 75, 50, 25, 10, or 5 microns or smaller). In someembodiments, the micro- or nanoparticles are about 3.2 microns orsmaller. In some embodiments, the ⁶LiF micro- or nanoparticles range insize from about 3.2 microns to about 200 nm (e.g., about 3.2, 3.1, 3.0,2.9, 2.8, 2.7, 2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6,1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9. 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, or 0.2microns). In some embodiments, nanoparticles are about 200 nm or less orabout 100 nm or less in size. For example, ⁶LiF nanoparticles that areabout 200 nm or about 100 nm or less can be prepared by size reductionof larger ⁶LiF microparticles or nanoparticles (e.g., ⁶LiF particlesthat are about 0.5 nm to about 10 microns in size). Size reduction canbe carried out, for instance, via ball milling (e.g., cryo ball milling)the larger particles for a period of time (e.g., 10 to 20 hours). Sizereduction of the particles can increase the transparency of the polymercomposite films prepared with the particles, increase interactions withneutrons, and better allow charged alpha and triton particles to escapeinto the polymer matrix, thus improving light emission. Accordingly,size reduction of the particles can increase light yield.

In some embodiments, the composite comprises ⁶Li salicylate or ⁶LiF as aneutron capture agent and P2VN as a matrix material. In someembodiments, the composite comprises ⁶LiF as a neutron capture agent andPEN or another aromatic polyester as a matrix material.

II.A.iii. Organic and Inorganic Luminescent Fluors

The presently disclosed composites can comprise organic and/or inorganicluminescent fluors. The term “fluor” as used herein refers to asubstance that displays fluorescence when excited by electromagnetic orparticular radiation. The organic or inorganic luminescent fluors of thepresently disclosed composites can act as energy harvesting antennamolecules to trap excitations from the matrix and to emit photons. Forexample, an excitation can hop from one aromatic moiety to another inthe polymeric matrix until it comes within a particular distance (e.g.,transfer radius) of the fluor, at which time the fluor traps theexcitation and subsequently emits a photon. The fluors can act as lightamplifiers when the composite materials are used as scintillationdetectors and can also act as wavelength shifters for improving theefficiency of the detectors. Thus, use of the fluors can increase thequantum yield of the composites (e.g, by allowing radiation at awavelength where the composite is more transparent).

Any suitable luminescent fluor can be used. In some embodiments, thefluor can be selected based on acceptor donor resonance, the lightemission characteristics of the fluor and/or its ability to resistoxygen and/or moisture induced scintillation quenching. In someembodiments, the fluor can be selected based on overlap between theexcitation spectra of the fluor and the emission spectra of the othercomponents of the composite (e.g., the polymer matrix).

Suitable luminescent fluors include, but are not limited to,2,5-diphenyloxazole (PPO), 1,4-bis-(5-phenyloxazol-2-yl) (POPOP),anthracene, 9,9,9′,9′,9″,9″-hexakis(octyl)-2,7′,2′,7″-trifluorene,n-terphenyl, 2-biphenyl-5-phenyl-1,3-oxazole,2-biphenyl-5(α-naphthyl)-1,3-oxazole,2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole,2-(4′-tert-butylphenyl)-5-(4″-biphenylyl)-1,3,4-oxadiazole,n-bis-(o-methylstyryl)-benzene 1,4-di-(5-phenyl-2-oxazolyl)-benzene,conjugated polymeric and oligomeric dyes, metal organic framework dyes,quantum dots, two-photon absorber semiconductor fluors and mixturesthereof.

III. Films

In some embodiments, the presently disclosed subject matter providesfilms of the presently disclosed polymer composites. The films can beused, for example, as thin scintillation detectors. The thinness of thefilms can allow secondary electrons to escape the scintillators,providing better neutron to gamma discrimination.

The composite films can be prepared by any suitable technique, such as,but not limited to, solution casting, hot pressing, and extrusion. Forexample, the film can be prepared by using an extruder such as, but notlimited to, a randcastle extruder with various processing conditions(e.g., various process zone temperatures, feed rate, die slitarrangements and opening size, take off rate, and downstream cooling ofthe extruded film) to increase the degree of crystallinity and/oroptical clarity of the film.

In some embodiments, the film can have a thickness of about 500 micronsor less (e.g., about 500, 450, 400, 350, 300, 250, 200, 150, 100, 75,50, 40, 30, 20, or 10 microns or less). In some embodiments, the filmhas a thickness between about 400 and about 200 microns. In someembodiments, the film has a thickness of about 220 microns or less. Insome embodiments, the film has a thickness of about 50 microns or less.In some embodiments, thicker films (>500 microns) can be used, forexample, when the neutron capture agent is provided as nanoparticlesthat are about 200 nm or less in size. In some embodiments, thepresently disclosed subject matter provides thin films of compositematerials where the films are as thick as about 1 millimeter. Thus, insome embodiments, the films can be about 1000, about 950, about 900,about 850, about 800, about 750, about 700, about 650, about 600, about550, or about 500 microns thick.

In some embodiments, the film can be biaxially or uniaxially stretched.The stretching can be performed by any suitable method, e.g.,mechanically or manually. In some embodiments, the stretching can bedone with a commercial film stretching machine. The stretching can beperformed using hot circulated air (e.g., at between about 120° C. andabout 150° C.). Stretching of the films below the matrix melting pointcan allow polymeric chains to orient. For example, in PEN-containingcomposite films (or other naphthalene-containing polymer compositefilms), strain induced stacking of naphthalene units can be obtainedmuch like a single crystal. Such stacking of naphthalene units canincrease the energy transport efficiency of the matrix. Addition ofexcitation harvesting luminescent molecules in stretched films canincrease the net quantum yield of the composite as compared to anunstretched film.

In some embodiments, the films or stretched films can be thermallyannealed. Any suitable annealing technique can be used, e.g., freeannealing, taut annealing, etc. In some embodiments, the films arethermally annealed, for example, between about 150° C. to about 180° C.(e.g., about 150, 155, 160, 165, 170, 175 or about 180° C.), usingconfined conditions using a ring or free annealing. Annealing the filmcan increase light yield when the film is used as a scintillator due toan increase in crystallinity of semi-crystalline polymer matrixmaterials, such as, but not limited to, polyethylene naphthalate (PEN).

In some embodiments, the film comprises a composite wherein the matrixmaterial is selected from the group comprising, but not limited to, apolyester, a polyamide, a polyether, a polyimide, a polythioester, avinylpolyether, a vinylpolyester, a vinylpolyamide, and avinylpolythioester, wherein the polymer comprises at least one aromaticgroup. In some embodiments, the matrix material is a polyester. In someembodiments, the polyester is selected from the group comprising, butnot limited to, polyethylene naphthalate (PEN), polytrimethylenenaphthalate (PTN), poly(9H-fluorene-9,9-dimethanol malonate),poly(9H-fluorene-9,9-dimethanol terephthalate), andpoly(4,4′-(9-fluorenylidene)-diphenol terephthalate).

In some embodiments, the film comprises a non-hygroscopic neutroncapture agent, e.g., ⁶LiF micro- or nanoparticles. In some embodiments,the film comprises a composite wherein the matrix material comprisesPEN, the neutron capture agent comprises ⁶LiF micro- or nanoparticlesand the film is a stretched film and/or thermally annealed film.

In some embodiments, the film comprises a polymer composite having aratio of matrix material to neutron capture agent of between about 5:1and about 1:5 by weight (e.g., about 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3,1:4, or 1:5). In some embodiments, the film has a ratio of matrixmaterial to neutron capture agent between about 3:1 and about 1:1 byweight. In some embodiments, the film comprises a ratio of matrixmaterial to neutron capture agent that is about 1:1 by weight. In someembodiments, the film comprises about 5% or less (e.g., about 5%, 4.5%,4%, 3.5%, 3%, 2%, 1.5%, 1%, or 0.5%) by weight of an organic orinorganic luminescent fluor. In some embodiments, the film comprises apolymer composite comprising about 49.5% by weight PEN, about 49.5% byweight ⁶LiF, and about 1% by weight9,9,9′,9′,9″,9″-hexakis(octyl)-2,7′,2′,7″-trifluorene. In someembodiments, the film comprises a polymer composite comprising about 70%by weight PEN, about 25% by weight ⁶LiF nanoparticles, and about 5%weight of a fluor or fluor mixture (i.e., PPO/POPOP).

Films of the presently disclosed subject matter can have a neutron countrate per mg of ⁶Li of between about 4 and about 12 counts per second(cps; e.g., about 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10,10.5, 11, 11.5, or 12 cps). In some embodiments, the neutron count rateper mg of ⁶Li is above that of a commercially available lithiated glassdetector, i.e., GS20 available from Applied Scintillation Technologies,Ltd., (Harlow, United Kingdom). Thus, in some embodiments, the neutroncount rate per mg of ⁶Li is above about 6.23.

In some embodiments, the film can be prepared by: providing a mixture ofan aromatic polymeric matrix material, a neutron capture agent, and aluminescent fluor; and hot pressing or extruding the mixture to form thefilm. In some embodiments, providing the mixture comprises preparingmicro- or nanoparticles of ⁶LiF; and mixing the micro- or nanoparticleswith the matrix material and the luminescent fluor (e.g., in the desiredweight ratios). In some embodiments, the film is further stretched(e.g., biaxially or uniaxially) and/or annealed.

IV. Apparatus

Referring now to FIG. 6, in some embodiments, the presently disclosedsubject matter provides an apparatus 10 for detecting neutron radiationwherein the apparatus comprises a photon detector 12 and a polymercomposite 14 (e.g., in the form of a molded coupon, film, fiber, orfiber mat). In some embodiments, polymer composite 14 comprises apolymeric matrix material comprising an organic polymer, copolymer orblend thereof. The polymer, copolymer or blend can comprise an aromaticmoiety (e.g., an aromatic moiety with high excitation transportefficiency like naphthalene and/or with a quantum yield higher thanphenyl). Polymer composite 14 can comprise a neutron capture agentcomprising a ⁶Li compound distributed within the matrix material and anorganic or inorganic luminescent fluor distributed within the matrixmaterial. Composite 14 can convert charged particles to light that canbe collected by a CCD or a PMT or other photon detector 12 efficientlyand at a fast rate. The composite can be structurally flexible, thusproviding capability for producing apparatuses with various geometriesand sizes. The apparatuses can be easily implemented in public placeswithout complications in operations.

Thus, in some embodiments, apparatus 10 can comprise a photon detector12 and a polymer composite 14 comprising: a polymeric matrix material,wherein the matrix material comprises an organic polymer, copolymer orblend thereof, and wherein the matrix material comprises at least onepolymer or copolymer comprising an aromatic moiety; a neutron captureagent distributed within the matrix material, wherein the neutroncapture agent comprises a ⁶Li compound; and an organic or inorganicluminescent fluor distributed within the matrix material. In someembodiments, polymer composite 14 is in the form of a film (i.e., anunstretched film, an uniaxially stretched film, or a biaxially stretchedfilm). In some embodiments, the film (e.g., the stretched film) isfurther annealed. In some embodiments, the film has a thickness of about500 microns or less (e.g., about 500, 450, 400, 350, 300, 250, 200, 150,100, 75, 50, 40, 30, 20, or 10 microns or less). In some embodiments,the film has a thickness between about 400 nm and about 200 microns.However, in some embodiments, the films can be as thick as about 1millimeter. Thus, in some embodiments, the films can be about 1000,about 950, about 900, about 850, about 800, about 750, about 700, about650, about 600, about 550, or about 500 microns thick.

In some embodiments, the polymer matrix is selected from the groupincluding, but not limited to, aromatic polyesters, polyamides,polyethers, polyimides, polythioesters, arylvinyl polymers(polyarylvinyls), vinylpolyesters, vinylpolyethers, vinylpolyamides andpolythioesters. In some embodiments, the polymer matrix does notcomprise polystyrene, polyvinyltoluene, or poly(phenylenevinylene). Insome embodiments, the polymer matrix includes an aromatic moiety otherthan phenyl or alkyl-substituted phenyl (e.g., methylphenyl). In someembodiments, the polymer matrix includes an aromatic moiety that has ahigher energy transport efficiency and/or quantum yield than phenyl. Insome embodiments, the aromatic moiety of the polymer is selected fromthe group including, but not limited to, naphthalene, anthracene,fluorine, terphenyl, phenanthrene, pyridine, furan, and thiophene. Insome embodiments, the matrix material is a polyester. In someembodiments, the polyester is selected from the group comprising, butnot limited to, polyethylene naphthalate (PEN), polytrimethylenenaphthalate (PTN), poly(9H-fluorene-9,9-dimethanol malonate),poly(9H-fluorene-9,9-dimethanol terephthalate), andpoly(4,4′-(9-fluorenylidene)-diphenol terephthalate).

In some embodiments, the neutron capture agent comprises ⁶LiF or ⁶LiSal.In some embodiments, the neutron capture agent comprises ⁶LiF micro- ornanoparticles.

Referring again to FIG. 6, photon detector 12 can be any suitabledetector or detectors and can be optically coupled to the scintillator(i.e., the polymer composite) for producing an electrical signal inresponse to emission of light from the scintillator. Thus, photondetector 12 can be configured to convert photons to an electricalsignal. Electronics associated with photon detector 12 can be used toshape and digitize the electronic signal. Suitable photon detectors 12include, but are not limited to, photomultiplier tubes, photodiodes, CCDsensors, and image intensifiers. Apparatus 10 can also includeelectronics 16 for recording and/or displaying the electronic signal.

V. Fibers and Fiber Mats

In some embodiments, the presently disclosed subject matter provides afiber comprising the presently disclosed polymer composites. Thus, insome embodiments, provided herein is a polymer composite comprising: apolymeric matrix material, wherein the matrix material comprises anorganic polymer, copolymer or blend thereof, and wherein the matrixmaterial comprises at least one polymer or copolymer comprising anaromatic moiety; a neutron capture agent distributed within the matrixmaterial, wherein the neutron capture agent comprises a ⁶Li compound;and an organic or inorganic luminescent fluor distributed within thematrix material.

The fibers can be prepared by any suitable method known in the art, suchas, but not limited to electrospinning, extrusion, meltblowing, and/ormeltdrawing. For example, in some embodiments, a solution of the matrixmaterial (or a precursor thereof, such as partially polymerizedmaterials), the neutron capture agent, and an organic or inorganicluminescent fluor can be prepared; and fibers can be prepared byelectrospinning, extruding, meltblowing, or meltdrawing the solution.The solutions can be prepared from any suitable solvent. In someembodiments, the solvent is chloroform, dimethylformamide (DMF),tetrahydrofuran (THF), or a mixture comprising two of more ofchloroform, DMF, and THF. In some embodiments, the solution comprisesabout 10 weight % by volume or less of the polymer matrix material(e.g., about 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1% by volume or less). Insome embodiments, the solution comprises about 5 weight % by volume ofthe polymer matrix material.

In some embodiments, the fibers have an average diameter of betweenabout 200 nm and about 500 microns. In some embodiments, the fibers havean average diameter between about 5 microns and about 500 microns. Insome embodiments, the fibers have an average diameter of between about200 nm and about 3.2 microns. In some embodiments, the fibers have anaverage diameter of between about 200 nm and about 1400 nm (e.g., about200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850,900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, and 1400 nm).In some embodiments, the fibers have an average diameter of betweenabout 400 and about 800 nm. In some embodiment, the fibers have anaverage diameter of 500 nm or less. In some embodiments, the fibers arenanofibers having an average diameter that is about 200 nm or smaller(e.g., about 150, 100, 75, 50, 40, 30, 20, 10, or 5 nm or smaller).

In some embodiments, the fiber is prepared from a polymer compositecomprising ⁶Li salicylate or ⁶LiF as the neutron capture agent. In someembodiments, the fibers are prepared from a polymer composite comprisingan aryl vinyl polymer (AVP) or an AVP blend as the matrix material;however, other polymers can also be used. In some embodiments, thematrix material is polystyrene (PS) or a blend ofpoly(2-vinylnaphthalene) (P2VN) and PS. The fibers can comprisenanophase domains (domains having diameters of less than about 50, 40,30, 20, 10, 5, 4, 3, 2, or 1 microns) of the neutron capture agentdistributed within the matrix. In some embodiments, the fluor isselected from the group comprising, but not limited to, PPO, POPOP, andanthracene. In some embodiments, the composite comprises between about10 and about 20 weight % of the neutron capture agent. In someembodiments, the composite comprises less than about 10% by weight ofthe fluor.

In some embodiments, fiber mats containing a plurality of the fibers canbe provided. The fiber mats are typically nonwoven, but can also bewoven, if desired.

VI. Methods of Detecting Neutron Radiation

In some embodiments, the presently disclosed subject matter provides amethod of detecting neutron radiation, wherein the method comprises:providing a polymer composite according to an embodiment of thepresently disclosed subject matter; disposing the polymer composite inthe path of a beam of radiation, wherein the matrix material and/or theluminescent fluor of the polymer composite emits light when thecomposite absorbs said radiation; and detecting neutron radiation bydetecting the light emitted by the composite, wherein the detectingdiscriminates between neutron and gamma radiation. The polymer compositecan be in the form of a film, a molded coupon, a fiber, or a fiber mat.In some embodiments, the polymer composite in is the form of a film. Insome embodiments, the film is biaxially or uniaxially stretched and/orthermally annealed.

In some embodiments, the method comprises the use of a suitable detectoror detectors optically coupled to the polymer composite for producing anelectrical signal in response to emission of light from the composite.Thus, in some embodiments, the method comprises using a photon detectorin combination with the polymer composite. Suitable photon detectorsinclude, but are not limited to, photomultiplier tubes, photodiodes, CCDsensors, and image intensifiers.

VII. Methods of Making Polymer Composites

In some embodiments, the presently disclosed subject matter provides amethod of making a film or a molded coupon comprising a polymercomposite of the presently disclosed subject matter. The method cancomprise: providing the neutron capture agent (e.g., providing micro- ornanoparticles of the neutron capture agent, such as micro- ornanoparticles of ⁶LiF); mixing the neutron capture agent (e.g., themicro- or nanoparticles of the neutron capture agent) with a polymericmatrix material and a luminescent fluor to form a mixture; and pressingand heating the mixture to form the film or molded coupon. Thus, in someembodiments, the presently disclosed subject matter relates to preparinga mixture (e.g., a solid powder mixture) of a matrix material (e.g., apartially polymerized resin or resin mixture of an organic polymer,copolymer or polymer blend or polymerizable monomers for the polymermatrix material), a neutron capture agent (e.g., micro- or nanoparticlesof a neutron capture agent), and an organic or inorganic luminescentfluor (e.g., a luminescent activator and/or a wavelength shifter); andhot pressing or extruding the mixture to form a film or a thick couponwherein the neutron capture agent and luminescent fluor are distributedwithin the matrix material (e.g., non-covalently encapsulated withinpores in the polymer matrix). Suitable extruders include, but are notlimited to, randcastle extruders. Processing conditions (e.g., processzone temperatures, feed rate, die slit arrangements and opening size,take off rate, downstream cooling, etc.) can be adjusted to increase thedegree of crystallinity and optical clarity.

In some embodiments, the matrix material is powdered (e.g., using a highspeed grinder) prior to mixing with the neutron capture agent and theluminescent fluor. In some embodiments, the mixture is ground in to apowder (e.g., using a high speed grinder) and sieved and/or blended(e.g., in a vortex mixer or by stirring or shaking mechanically ormanually) to obtain a homogenous mixture. In some embodiments, themixture is sieved through a 500 μm or smaller sieve (e.g., through a500, 450, 400, 350, 300, 250, 200, 150, 100, 50 μm or smaller sieve).

In some embodiments, the neutron capture agent is ⁶LiF micro- ornanoparticles that are 3.2 microns or smaller in diameter. The ⁶LiFmicro- or nanoparticles can be provided, for example, by titrating⁶Li-enriched lithium hydroxide with hydrofluoric acid to precipitate⁶LiF particles, and collecting the precipitated particles (e.g., byvacuum filtration). The collecting can also include washing (e.g., withwater) the particles to remove impurities and/or drying the particles.

In some embodiments, the neutron capture agent is ⁶LiF nanoparticlesthat are about 200 or about 100 nm or smaller. The ⁶LiF nanoparticlescan be prepared by pulverizing larger ⁶LiF particles (e.g., ⁶LiFparticles that are about 0.5 to about 10 microns or about 1 to about 3microns in size). The pulverizing can be performed by, for example, byball milling (e.g., cryo ball milling) the larger ⁶LiF particles for aperiod of time (e.g., between about 10 to 20 hours) to achieve thedesired size reduction.

In some embodiments, pressing and heating the mixture comprises heatingthe mixture to a temperature of between about 260° C. and about 300° C.(e.g., about 260, 270, 280, 290, or 300° C.). In some embodiments, thefilm can be stretched (e.g., uniaxially or biaxially). The stretchingcan be performed manually or mechanically. In some embodiments, thestretching is performed using a commercial film stretcher. In someembodiments, the stretching is performed at a temperature between about120° C. and about 150° C. (e.g., at about 120, 125, 130, 135, 140, 145,or 150° C.). In some embodiments, the film can be thermally annealed,for example, at a temperature between about 150° C. and about 180° C.(e.g., at about 150° C., 155° C., 160° C., 165° C., 170° C., 175° C. or180° C.). The annealing can increase the crystallinity of the composite.

In some embodiments, the film can be prepared by solution casting asolution comprising the matrix material, the neutron capture agent andthe luminescent fluor. In some embodiments, the solution comprises THF,DMF, chloroform, or mixtures thereof. In some embodiments, the presentlydisclosed subject matter relates to a microwave-based high pressurevolumetric heating process to obtain ⁶LiF distribution within a polymermatrix by completely dissolving ⁶LiF and a polymer fluor system in acommon solvent. In some embodiments, the solution cast film can bestretched (biaxially or uniaxially) and/or thermally annealed.

EXAMPLES

The following Examples have been included to provide guidance to one ofordinary skill in the art for practicing representative embodiments ofthe presently disclosed subject matter. In light of the presentdisclosure and the general level of skill in the art, those of skill canappreciate that the following Examples are intended to be exemplary onlyand that numerous changes, modifications, and alterations can beemployed without departing from the scope of the presently disclosedsubject matter.

Example 1 Synthesis of Poly(4,4′-(9-fluorenylidene)-diphenolterephthalate)

In a vial with a septum and a stir-bar, 4,4′-(9-fluorenylidene)-diphenol(1.2615 g, 3.6 mmol) is dissolved in THF (8 mL), and pyridine (0.6 mL,7.2 mmol) is added. The vial is sealed, evacuated using an aspirator,and refilled with argon. This evacuation and refilling is repeated twomore times. In a separate vial with a septum, terephthaloyl chloride(0.7308 g, 3.6 mmol) is dissolved in THF (3 mL). The vial is sealed,evacuated and refilled with argon like above. While stirring, the diolsolution is heated to 65° C., and the acid chloride solution is addeddrop-wise with a syringe over about ten minutes. The mixture is thenallowed to stir for an additional hour. Upon cooling, the polymermixture is dropped into vigorously stirred methanol (120 mL). Theprecipitated polymer is then suction filtered and dried in a vacuumdesiccator. White polymer is obtained. A typical yield is 70 to 80%.

Example 2 Vinylpolyester and Vinylpolythioester Synthetic Procedure

Methacryloyl chloride is dissolved in THF in a vial with a septum and astir bar. The vial is evacuated and refilled with argon three times.Equimolar amounts of an alcohol or thiol and pyridine dissolved in THFare added drop-wise with a syringe to the methacryloyl chloridesolution. The solution is stirred for one hour and/or until formation ofthe vinyl monomer with ester-linked side group is complete (e.g., asdetermined by thin layer chromatography or by gas or liquidchromatography). A solution of azobisisobutyronitrile (AIBN) in THF isthen added to the vial with a syringe to initiate polymerization, andthe solution is heated overnight at a temperature of 70 to 80° C. Thepolymer is then precipitated in methanol, filtered, and dried.

Example 3 Poly(2-Vinylnaphthalene) Composite Films

⁶Li-salicylate (⁶LiSal) was prepared by dissolving salicylic acid inacetone and heating it to 60° C. ⁶LiOH monohydrate was dissolved in a2:1 mixture of acetone and deionized water and sonicated for 10 minutes.Then the salicylic acid solution was titrated by adding the ⁶LiOHsolution dropwise. The resulting solution was kept at 60° C. withstirring for 18 hours to evaporate the solvent. The resulting whitepowder was dried in a vacuum oven at 60° C. for 72 hours.

Solutions containing varying amounts of poly(2-vinylnaphthalene) (P2VN;Polymer Source, Inc., Dorval, Quebec, Canada) and ⁶LiSal in 1.5 mLanhydrous THF were placed under vacuum to remove dissolved air andstored under an argon atmosphere. Films were cast in a glove bag in adry nitrogen atmosphere. THF was evaporated and the films dried in avacuum at 50° C. to remove any residual solvent. Translucent films about46 mm in diameter, with thicknesses ranging from 85 to 110 microns wereobtained. Some phase separation was detected by optical microscopy,which showed what appeared to be ⁶LiSal domains separated within theP2VN matrix. It is also possible that pores formed in the polymer matrixduring solvent evaporation. It is expected that broadening the molecularweight distributions of the polymer to include shorter chains asplasticizers and/or limiting the thickness of the cast films can reducephase separation and pore formation.

Thin film samples (110 microns thick) of equal weight and composition ofP2VN and polyvinyl toluene (PVT) doped with 25 weight % ⁶LiSal (butwithout additional fluor) were prepared as described above for P2VNfilms. Thin films can be exposed to radiation flux using acrylic andcadmium cylinders as described in Sen et al. (IEEE Transactions onNuclear Science, 58(3), 1386-1393 (2011)). Superior light output wasobserved with the P2VN based detector. Pure P2VN and PVT films without⁶LiSal were exposed to the same radiation flux and did not show anyscintillation response. There were no major changes in P2VN fluorescencespectra of samples that were held under nitrogen as compared toair-equilibrated samples, indicating that the detectors were stable tooxygen.

Films having equal total weight (200 mg), but different weight % of⁶LiSal and different thicknesses were prepared and subjected to thermalneutron flux. See Table 1, below. The best composition based on relativelight output observed was 25 weight % ⁶LiSal.

TABLE 1 Relative Light Output of ⁶LiSal/P2VN Films Relative Light OutputIntegral Film Wt % using Cf-252 Count Rate Thickness Sample ⁶LiSal(relative to sample 3) (Counts/sec) (μm) 1 10 0.70 32.4 94 2 15 0.7037.9 92 3 25 1.00 45.7 89 4 40 0.70 63.0 85 5 50 0.60 74.5 82 6 60 0.3085.0 79 7 75 0.25 76.1 75

To increase the thickness of the detectors, multiple layers of filmswere stacked. Each film had a composition of 22 weight % ⁶LiSal and 2weight % of an additional fluor,9,9,9′,9′,9″,9″-hexakis(octyl)-2,7′,2′,7″-tetrafluorene (i.e., ADS038FO,from American Dye Source, Inc., Baie-D'Urfé, Quebec, Canada). Thecomposite films had an emission peak at 420 nm (matching the emissionpeak for the fluor) when excited with 270 nm light, demonstratingefficient energy transport and migration from naphthalene to the fluor.The decay time for the film was 3 ns, matching the decay time of thefluor. The net neutron response for stacking up to four films is shownin Table 2, which includes comparative data from a 2 mm lithiated glassscintillator GS20 (Applied Scintillation Technologies, Ltd., Harlow,United Kingdom).

TABLE 2 Multilayer ⁶LiSal/P2VN Detectors Number of Scintillator MassRelative Light Output Integral Count Layers (mg) using Cf-252 Rate(Counts/sec) 2 mm GS20-2460 1 653.7 thick disk 1 120 1.17 14.4 2 2041.02 19.6 3 290 0.97 32.7 4 411 0.87 52.3

As can be seen from Table 2, neutron sensitivity of GS20 is an order ofmagnitude higher as compared to the composite films. However, withoutbeing bound to any one theory, it is believed that this is due at leastin part to the matrix being an amorphous polymer and the composite beingopaque. The light output of the composite films was comparable to GS20.

Example 4 Polyester/⁶LiF Composite Thin Films

⁶LiF particles were synthesized by titration of lithium-6 enrichedlithium hydroxide (prepared by dehydrating 97.6% ⁶Li lithium hydroxidemonohydrate) with hydrofluoric acid as shown in the equation:

⁶LiOH+HF→⁶LiF+H₂O

The ⁶LiF particles were examined with a scanning electron microscope(SEM). Image processing and measurements of the particle size wereperformed with the ImageJ image software program (available on theinternet from the National Institutes of Health). The synthesizednanoparticles had sizes between at least 0.1 microns and 3.2 microns,with a modal size of 750 nm.

Polyethylene naphthalate (PEN) pellets (available from GoodfellowCorporation, Oakdale, Pa., United States of America) were ground topowder with a commercial grinder and sieved through a 150 μm sieve. ThePEN powder was mixed with ADS156FS dye (American Dye Source, Inc.,Baie-D'Urfé, Quebec, Canada) and ⁶LiF nanopowder for 10 minutes in avortex mixer. Circular samples were pressed within kapton sheets in ahot press at 300° C., providing films of 50 mm diameter and varyingthicknesses. SEM imaging of the films showed a featureless surface,while dark field microscope imaging indicated that the ⁶LiF particleswere non-agglomerated and fairly well distributed within the PEN matrixat 35 weight % loading.

Scintillation measurements were made using three sample composite thinfilm detectors comprising 25 weight % ⁶LiF, 74 weight % PEN, and 1weight % ADS156FS dye and compared to measurements taken using a 2 mmthick lithiated glass disc scintillator (GS20, Applied ScintillationTechnologies, Ltd., Harlow, United Kingdom). Scintillation measurementswere performed as described in Sen et al. (IEEE Transactions in NuclearScience (2012), vol. 59(4), 1781-1786). The net thermal neutron countrate for a 220 μm thick 480 mg PEN composite film was 505 counts persecond (cps), while that for a 150 thick 375 mg PEN composite film was426 cps, that for a 66 μm thick 120 mg PEN composite film was 74 cps,and that for the glass disc scintillator was 498 cps. Thus, thecomposite films had comparable count rates to GS20. The responses of thefilms to alpha, beta and gamma radiation were also determined. There wasa lack of a Compton edge on the gamma spectrum for the films. Withoutbeing bound to any one theory, this lack is believed to be due tosecondary electrons not depositing their energy in the film as theCompton electrons are escaping the thin film.

There was separation between the neutron and gamma spectra for thesample films, providing the potential for discrimination based on pulseheight. The neutron efficiency and count rates at various gammaefficiency pulse height discriminator levels are shown in Table 3,below, for the 150 μm thick film and in Table 4, below, for the 66 μmthick film.

TABLE 3 Intrinsic efficiencies of a 150 μm thick PEN/⁶LiF compositefilm. Gamma Intrinsic Neutron Intrinsic Neutron LLD Setting EfficiencyEfficiency Count Rate 226 5 × 10⁻² 0.4047 423 1276 5 × 10⁻³ 0.2909 3042676 5 × 10⁻⁴ 0.1734 179 4176 5 × 10⁻⁵ 0.0469 47.8

TABLE 4 Intrinsic efficiencies of a 66 μm thick PEN/⁶LiF composite film.Gamma Intrinsic Neutron Intrinsic Neutron LLD Setting EfficiencyEfficiency Count Rate 176 5 × 10⁻² 0.0705 74 926 5 × 10⁻³ 0.0682 72 20265 × 10⁻⁴ 0.0556 59 3976 5 × 10⁻⁵ 0.0239 26 5676 5 × 10⁻⁶ 0.0016 1.9

Example 5 Stretched Polyethylene Naphthalate (PEN)/⁶LiF Composite ThinFilms

Film Preparation:

PEN was purchased from Goodfellow Corporation (Oakdale, Pa., UnitedStates of America). The ADS156FS luminescent molecule (chemical formulaC₁₁₂H₁₃₆O₂S, American Dye Source, Inc., Baie-D'Urfé, Quebec, Canada) wasused to increase the quantum yield of the composite and selected basedon its high quantum yield, resonance energy transport ranges andresistance to luminescence quenching in the presence of moisture. PurePEN resin had an excitation maximum at 258 nm and an emission peak at430 nm. The decay times for pure PEN were 6 ns and 19 ns. ADS156FS hasan absorption peak at 382 nm, photoluminescent maximum at 432 nm anddecay time of 3 ns.

⁶LiF nanoparticles were synthesized as described above in Example 4. Thesynthesized nanoparticles had a modal size of 750 nm.

PEN chips, ⁶LiF nanoparticles and ADS156FS were mixed in a weight ratioof 49.5:49.5:1 PEN:⁶LiF:ADS156FS, ground into a powder in a high speedgrinder, sieved through a 150 μm sieve, blended in a vortex mixer forten minutes to obtain a homogeneous blend, and dried in vacuum at 110°C. The mixture was weighed and formed into a film on a hot press at 280°C. at 1.7×10⁷ Pascal (Pa). For comparison, PEN chips alone weresubjected to grinding, sieving, blending and drying and also formed intoa pure PEN film using the hot press.

The pure PEN and composite films were biaxially stretched by 1.5×1.5 onan AccuPull™ laboratory biaxial film stretcher (Inventure LaboratoriesIncorporated, Knoxville, Tenn., United States of America) which drew thefilm simultaneously in the machine direction (MD) and the transversedirection (TD) in a single step. Stretching can cause orientation of thepolymer chains in the direction of the stretch and improve thecrystallization of the film. Circular samples 50 mm in diameter were cutfor analysis. The thicknesses of the films were as follows: unstretchedpure PEN film, 75 microns; biaxially stretched pure PEN film 43 microns;unstretched composite PEN film, 150 microns; biaxially stretchedcomposite PEN film, 41 microns.

Emission and excitation spectra of the film samples were characterizedon a Hitachi F4500 fluorescence spectrophotometer at a voltage of 400volts and slit of 2.5 mm. Transmission spectra of the film samples werecharacterized on a Cary WinUV spectrophotometer. The alpha, beta, gammaand neutron response of the film samples were characterized andscintillation measurements were made as described in Sen et al. (IEEETransactions in Nuclear Science (2012), vol. 59(4), 1781-1786). Alpha,beta, gamma and neutron response for the pure and composite PEN filmswere measured at 1200V. A GS20 glass disc scintillator (AppliedScintillation Technologies, Ltd., Harlow, United Kingdom) having adiameter of 25 mm, a thickness of 2 mm, and a mass of 2.461 g was usedfor comparison.

Transmission Spectra:

The biaxially stretched composite PEN films appear to be moreluminescent in UV light than unstretched pure PEN or biaxially stretchedpure PEN films. The transmission spectra of the pure and composite filmsshowed that UV light is strongly absorbed below 380 nm. Unstretched purePEN film had a high optical transmittance (between 50% and 80% in thevisible region), and the film appeared translucent. Stretched pure PENfilm has optical transmission between 63% and 69% in the visible region.Biaxially stretched composite PEN films had no transmission. This lackof transmission is believed to be due, at least in part, to very highloading of ⁶LiF, which is opaque and also causes light scattering (whichcould not be detected by the small detector of the instrument). Allthree films appeared translucent under natural light. Biaxiallystretched pure PEN film was the most transparent, as it had a lesserthickness than the unstretched pure PEN film and did not contain ⁶LiF.

Emission Spectra:

Unstretched PEN film, which is amorphous, emits fluorescence. SeeFIG. 1. The emission spectra are mirror images of absorption spectra ofPEN, and fluorescence occurs from the lowest energy level of thesinglet-excited states. The fluorescence peak at about 380-390 nm of thepure PEN film spectra is assigned to monomer fluorescence because of itscoincidence with that of dimethyl 2,6-naphthalate, whereas the peakaround 420-430 nm was assigned to be excimer fluorescence because theexcitation spectrum monitored at 430 nm coincided with that for themonomer fluorescence.

Emission spectra of unstretched PEN film and biaxially stretched PENfilms excited at 310 nm show peaks at 434-436 nm, whereas biaxiallystreteched composite PEN films excited at 310 nm show peaks at 466-468nm. See FIG. 1. The fluorescence spectrum of naphthalene shows emissionat 323 nm and 335 nm. The high-energy charged reaction products canexcite electrons in the aromatic group of the polymer matrix of thescintillation detector and can generate secondary electrons. It appearedthat the PEN excimers can have an excited level corresponding to theemission peaks of 434-436 nm. The excitons can either produce photonsdirectly through excimer emission or can harvested by the luminescentmolecules that concomitantly emit photons at a longer wavelength thanthe polymer matrix.

Excitation Spectra:

Excitation spectra of unstretched PEN film and biaxially stretched PENfilms observed at 430 nm show absorption band peaks at 285-286 nm and375-379 nm, whereas biaxially stretched composite PEN films observed at430 nm show two absorption band peaks, one at 287 nm and second bandpeaks at 372 nm, 400 nm, and 427 nm. See FIG. 2. The fluorescencespectrum of naphthalene showed excitation at 266 nm, 275 nm, and 285 nm.

The absorption band peaks of biaxially stretched composite PEN films areshifted toward longer wavelengths because of the presence of wavelengthshifting fluor. The absorption peaks correspond with the excitationpeaks. The peak with a maximum at 413 nm and two shoulders at 392 nm and430 nm is attributed to the fluorescence of an excimeric configurationof the PEN molecule. PEN can exhibit a low rate of intersystem crossingof the monomeric unit. See Cheung et al., Appl. Polym. Sci., 24,1809-1830 (1979).

Neutron Response:

Thermal neutrons interact with ⁶Li and produce charged a particles andtriton with kinetic energy sufficient to excite the aromatic units ofthe PEN of the scintillation detector. The energy released as kineticenergy during neutron capture by ⁶Li is split into 2.73 MeV for thetriton and 2.05 MeV for the α particle. The neutron count rates of thePEN films are presented in Table 5, below, and the neutron count spectraare shown in FIG. 3. The count rates for stretched and unstretchedcomposite films were compared to that of a 2 mm thick lithiated glassscintillator (GS20, Applied Scintillation Technologies, Ltd., Harlow,United Kingdom). The choice of amplifier time constant determines thedegree of charge collection from the tube. Time constant of 2 μs orgreater resulted in nearly complete charge collection and yield spectra.The unstretched composite PEN film with a mass of 521 mg had a countrate of 265 cps, whereas the stretched composite PEN film with a mass of76 mg had a count rate of 62 cps. The GS20 had a count rate of 442 cps.A significant increase (60%) in the count rate per mg ⁶Li was observedfor the stretched composite film as compared to the unstretchedcomposite film. The count rate per mg ⁶Li of the stretched compositefilm was found to be higher than that for GS20.

Without being bound to any one theory, a scintillation detector withhigh crystallinity is believed to be capable of capture of higherincident high-energy particles to generate a greater number of photons.The efficiency of singlet-singlet energy transfer given in steady-stateexperiments depends, for example, upon excitation energy, which isbrought into the neighborhood of the luminescent molecule singlet levelby the naphthalene singlet band, luminescent molecule/polymerfluorescence ratio, excitation exchange interactions, the lifetime, theluminescent molecule/polymer energy difference, the temperature, andsystem defects and impurities. See Argyfukis and Kopelman, ChemicalPhysics, 51, 9-16 (1980). A crystal provides a highly efficient energytransport system to luminescent molecules as it has has fewer defectsites or imperfections in the lattice. Defect sites or imperfections canact as traps for the annihilation of excitons. See Ratnera et al.,Nuclear Instruments and Methods in Physics Research A, 486, 463-470(2002). The luminescent molecules within the presently disclosed polymermatrix can harvest the resonant energy transferred (RET) from excitednaphthalene molecules and emit photons. RET depends upon the degree ofspectral overlap, distance and the orientation of transition momentsbetween the luminescent molecule and the polymer. See Andrews, Can. J.Chem., 86, 855-870 (2008).

TABLE 5 Neutron Performance of PEN Films Count Count Mass ⁶Li Neutronrate rate per Sample Mass (mg) (mg) Peak (cps) mg ⁶Li Unstretched 52162.52 ~3000 265 4.24 composite PEN film Stretched 76 9.12 ~2000 62 6.80composite PEN film GS 20 — 71.00 7,342 442 6.23

A broad neutron peak for unstretched composite PEN film was observed atapproximately 3000, whereas a broad neutron plateau was observed forstretched composite PEN film. An unstretched film had a thickness of 150μm and is thick enough to capture the energy deposited by chargedreaction products but the stretched composite PEN film had a thicknessof 41 μm, which is less than the range of charged reaction products. Soit is believed possible that the charged reaction products do notdeposit the full energy in the stretched film. The energy deposited bycharged reaction products within the crystals is efficiently transportedby luminescent molecules, which produced net radioluminescence responsewith lower pulse height deficit.

Neutron-gamma discrimination curves for unstretched and stretchedcomposite PEN films are shown in FIGS. 4A and 4B. The stretchedcomposite PEN film showed better discrimination. The effect of energydeposited by gamma and charged particles became clearly separableleading to thermal neutron discrimination because of the lower thicknessof the stretched composite PEN film. The low pulse height from gamma-rayevents can be due to secondary electrons that are knocked off by gammarays to escape thin detectors. The stretched composite PEN films appearto have low susceptibility to gamma-induced scintillation and thus canbe effective discriminators for thermal neutrons. At low LLD settings,the electronic system is paralyzed by the processing of low amplitudenoise, while at high LLD values, the count rate decreases due to theloss of neutron detection events. Based on FIGS. 4A and 4B, if the LLDis set at 3000 for the stretched composite PEN films, neutron-gammadiscrimination can be established and yields the possibility ofdiscrimination based on pulse height. However, suitable LLD settings canvary depending upon the gain used for a given PMT, scintillationmaterial composition, and attachment settings.

Alpha, Beta and Gamma Response:

Pulse height spectra were obtained by exposing the unstretched andstretched pure and composite PEN films to alpha (²⁴¹Am), beta (³⁶Cl),and gamma (⁶⁰Co) particles. See FIGS. 5A, 5B, and 5C, respectively. Thephotoelectron yield is the number of photoelectrons created at thephotocathode of the PMT. The total number of the counts in the photopeakcan be calculated from the area under the spectral curve in thephotopeak zone. The light yields of various PEN films are provided inTable 6. All values are scaled to 1200 V, 500. The GS20 ⁶⁰Co measurementreported is the Compton edge.

TABLE 6 Light Yield of Stretched vs. Unstretched PEN Films. ²⁴¹Am ³⁶ClEnd ⁶⁰Co End Sample Peak point Point Unstretched Pure PEN 3,095 2,5122,080 Stretched Pure PEN 1,703 1,107 1,559 Unstretched Composite PEN2,256 1,904 2,831 Stretched Composite PEN 1,706 1,706 5,327 GS20 4,0026,740 5,530

The stretched composite PEN film had about 30% higher light output thanunstretched composite PEN film. See FIG. 5A. Stretched film samples wereapproximately one fourth as thin as unstretched composite PEN films, sothe alpha particles were not able to deposit on the stretched films asmuch. However, as the stretched composite PEN film had highercrystallinity, which results in more efficient energy transport toluminescent molecules, it generated a higher number of photons ascompared to unstretched composite PEN film.

Stretched composite PEN films have low alpha to beta ratio and henceneutron/gamma discrimination. The low gamma-ray sensitivity can be dueto the high thermal-neutron capture cross-section, the large 4.78 MeVenergy of the reaction products and the thinness of the detectors.Thicker PEN films have more interactions than the thinner PEN films.Photopeaks were observed at less than 500 keV by the film samples as thesecondary electrons at higher energy had greater probability to escapewithout deposition of energy in the 41 to 150 micron film samples.

Compton scattering was observed for unstretched composite PEN films andwas absent in the case of stretched composite PEN films. Lack of Comptonscattering can be attributed to non-deposition of the energy of theelectrons in the thinner stretched composite PEN films. The broadness ofthe photopeaks can also be due to the thin samples or from an increasein the transfer resolution due to the optical transmission of thesample. Pulse height spectroscopy of a thicker unstretched composite PENfilm sample yielded a smaller photopeak, suggesting that light yield wassignificantly degraded due to poor light propagation in the sample.Scattered light trace out a longer distance and therefore will beattenuated to a greater extent in the presence of impurities andquenching.

Conclusions:

Unstretched and stretched pure as well as composite PEN films embeddedwith ⁶LiF and a wavelength shifting luminescent molecule werefabricated. The stretched composite detectors effectively discriminatebetween thermal neutrons and gamma radiation, due at least in partbecause the film samples were thin (in some embodiments having athickness of 41 microns). Low atomic number components have lowsusceptibility to gamma-induced scintillation and thus are effectivediscriminators for thermal neutrons. The effect of energy deposited bygamma and charged particles became clearly separable leading to thermalneutron discrimination because of the higher degree of crystallinity inthe scintillation detector. Stretched composite PEN films have low alphato beta ratio and hence, neutron/gamma discrimination due to highercrystallinity. A 60% increase in the count rate per mg ⁶Li was observedfor the stretched composite film as compared to the unstretchedcomposite film. The count rate per mg ⁶Li of stretched film was found tobe higher than that for a ⁶Li-based transparent glass detector (GS20).The stretched composite PEN film had about 30% higher light output thanunstretched composite PEN film. The energy deposited by chargedparticles within such oriented molecules is efficiently harvested byluminescent molecules, which produced net radioluminescence responsewith lower pulse height deficit.

Example 6 Annealed Composite Films Comprising ⁶LiF Nanoparticles

Synthesis of LiF Nanoparticles:

⁶LiOH was dissolved in methanol to remove impurities. The impurities areinsoluble in methanol and can be collected on a filter paper. Themethanol was evaporated and the purified ⁶LiOH collected.

The dried purified ⁶LiOH was dissolved in de-ionized water by vigorousstirring (at about 350 to 400 rpm) for about 30 to 60 minutes. Oncedissolution was complete, the ⁶LiOH solution was treated with a solutionof hydrofluoric acid (HF) according to the equation:

⁶LiOH+HF→H₂O+⁶LiF

The resulting liquid was then poured into a cold acetone bath andsubsequently filtered. All reactions were performed in TEFLON™ (E.I.DuPont de Nemours and Company, Wilmington, Del., United States ofAmerica) beakers to avoid silicon impurities in the final product. Theacetone mixture was vacuum filtered through a 1 μm filter paper. Thefiltrate was collected and retained, while the filtrant was allowed todry. The filtrate was then passed through a 450 μm filter paper. Theresulting filtrate was allowed to dry.

Resulting ⁶LiF particles were subjected to cryo ball milling for 10 to20 hours to provide nanoparticles of very small sizes (i.e., less than100 nm).

Processed Composite Films:

Composite films were prepared by mixing about 25 weight % of the ⁶LiFnanoparticles, about 70 weight % PEN, and about 5 weight % PPO/POPOP andthen blending the mixture in a vortex mixer to obtain a homogenousblend. The homogenous blend was dried in a vacuum. The dried blends wereweighed and formed into cast composite polymer films.

Unstretched cast composite films (UCFs) were post processed by differenttechnologies. In particular, the UCFs were annealed at 150° C. toprovide processed composite polymer films (PCFs). Circular samples of 50mm diameter size were cut from the UCFs and PCFs for furthercharacterization.

Tables 7 and 8 below show the impact of post-processing on neutron countrate and brightness. For comparison with the UCFs and PCFs, data is alsoprovided for a 2 mm commercial lithiated glass scintillator (GS20;Applied Scintillation Technologies, Ltd., Harlow, United Kingdom). Anincrease of between 70% to 90% in neutron count rate above gamma LLD anda 40% increase in brightness was observed for the PCFs compared to theUCFs. Neutron count rate above gamma LLD for the PCFs was three to fivetimes higher than that for GS20. Without being bound to any one theory,it is believed that the post-processing provides increased crystallinityin the composite films, which can increase their efficiency in detectingthermal neutrons and in neutron-gamma discrimination.

TABLE 7 Neutron Performance Gamma LLD such that ξ_(int) Neutron Countrate Sample γn < 10⁻⁶ above ξ_(int) γn < 10⁻⁶ (thickness) (ChannelNumber) (cps) UCF (158 μm) 3702 12.50 PCF (158 μm) 5053 21.20 UCF (167μm) 3879 7.19 PCF (167 μm) 5525 13.51 GS20 (2000 μm) 4000 4.5

TABLE 8 Film Brightness Neutron End Point Sample (Channel Number) UCF(140 μm) 2031 PCF (140 μm) 2823 GS20 (2000 μm) 4087

FIG. 7 shows gamma (⁶⁰Co) and net thermal neutron (²⁵²Cf) responses forthe UCFs and PCFs (i.e., for 44.2 mg mass samples, with film thicknessesof 340 microns). For comparison, gamma and net thermal neutron responseis also shown for a GS20 sample (2.47 grams, 2.1 mm). If the count ratesare normalized for ⁶LiF amount, the thin film composites have asignificantly higher count rate per mg of ⁶LiF than the lithiated glassscintillator.

An additional, thicker (490 microns) cast composite film comprising 70weight % PEN, 25 weight % ⁶LiF nanoparticles, and 5 weight % PPO/POPOPwas prepared. The film was cut into two inch diameter samples. Onesample was post processed via thermal annealing as described above. Bothan unstretched, non-annealed sample (UCF, 490 microns) and the postprocessed sample (PCF, 490 microns) were characterized for neutron andgamma response. See FIG. 8. See also, Table 9, below. For comparison,results for the commercial lithiated glass scintillator (GS20; 2100microns thick) are also shown. Both composite samples had a mass of 1.02g, while the glass scintillator had a mass of 2.47 g.

TABLE 9 Neutron and Gamma Responses of 490 Micron Thick Composite Films.Neutron Count Rate Neutron Count Neutron above Gamma LLD Mass CountRate/mg End Point such that ⁶Li Rate ⁶Li (Channel ξ_(int) γn < 10⁻⁶Sample (mg) (cps) (cps/mg) Number) (Channel Number) GS20 154.2 280 24244 2 UCF 61.2 286 5 1949 2 PCF 61.2 280 5 2873 9

Example 7 Electrospun Polymer Nanofibers

Polymer composite nanofibers can be prepared as follows. Briefly, asolution of high molecular weight PS (M_(n)=10⁶ as determined by gelpermeation chromography) and P2VN (M_(n)=1.2×10⁶) was prepared inanhydrous THF/DMF (4:1 v/v) by mixing the polymer and solvents (3 weightby volume PS and 2 weight % by volume P2VN) and heating the mixture to75° C. for 90 minutes until a homogenous solution was obtained. Asolution of the high molecular weight PS (3 weight % by volume) wasprepared in anhydrous CHCl₃/DMF (17:3) by mixing the polymer andsolvents and heating the mixture to 75° C. for 90 minutes until ahomogenous solution was obtained. To the PS/P2VN solution was added⁶LiSal (13.5 weight % in polymer) and anthracene (7 weight % inpolymer). To the PS solution was added ⁶LiF (20 weight % in polymer) andPPO/POPOP (8 weight % in polymer). The polymer solutions wereelectrospun using 3 mL and 5 mL syringes, having 16.5 gauge (for the PSsolution) and 23 gauge (for the PS/P2VN solution) needles. A meteringpump delivered polymer solution through the syringe to the tip of theneedle. A direct current high voltage power supply was used to applyvoltage (16 kV-18 kV) to the needle, producing a jet toward a groundedcollector.

For characterization by energy dispersive X-ray-scanning electronmicroscopy or scanning electron microscopy, the fibers were coated withgold using a sputter coater. The fibers had diameter size distributionsbetween 200 and 1400 nm. The fiber distribution and average fiberdiameter (505 nm) of the ⁶LiF/PS fibers were slightly narrower andsmaller than the fiber distribution and average fiber diameter (515 nm)of the ⁶LiSal/PS/P2VN fibers. Without being bound to any one theory, itis believed that an increase in polymer concentration can increase theaverage nanofiber diameter, while the dielectric properties and surfacetension of the solution solvents can influence the phase morphology andfiber dimensions. In one larger diameter fiber, micron size crystals(approximately 3 microns) were observed distributed within the PSfibers.

The excitation-emission behavior of fiber mats of the ⁶LiF/PS and⁶LiSal/PS/P2VN nanofibers were studied. The ⁶LiF/PS nanofiber mat had anexcitation peak at 280 nm and an emission peak at 420 nm with a Stokesshift of 140 nm. The ⁶LiSal/PS/P2VN nanofiber mat had an excitation peakat 313 nm and an emission peak at 432 nm with a Stokes shift of 119 nm.The emission curve of the ⁶LiSal/PS/P2VN nanofiber mat had a singlepeak, corresponding to the emission of anthracene, indicating efficientintermolecular energy transport.

The samples were tested under irradiation with alpha, beta and gammasources using a neutron irradiator containing acrylic and cadmiumcylinders to obtain a net thermal neutron response as described in Senet al. (IEEE Trans. Nucl., Sci. 58(3), 1386-1393 (2011)). The⁶LiSal/PS/P2VN nanofiber mat had clear distinction of thermal neutrons.See Young et al. (Journal of Engineering Materials and Technology, 134,010908 (2012). Although the neutron response was not as large as forGS20, the nanofiber mat had a significantly lower loading of ⁶Li, wasthinner and had a smaller net weight. Neutrons were not detected for the⁶LiF/PS fiber mats. Without being bound to any one theory, this isbelieved to be due to quenching of light and to micron-sized domainsscattering light within the samples. The fiber mats did not yieldappreciable light response using alpha, beta, or gamma rays. This wasexpected due to the small amount of neutron absorbing material in themats.

It will be understood that various details of the presently disclosedsubject matter may be changed without departing from the scope of thepresently disclosed subject matter. Furthermore, the foregoingdescription is for the purpose of illustration only, and not for thepurpose of limitation.

What is claimed is:
 1. A polymer composite comprising: a polymeric matrix material, wherein the matrix material comprises an organic polymer, copolymer or blend thereof, and wherein the matrix material comprises at least one polymer or copolymer comprising an aromatic moiety; a neutron capture agent distributed within the matrix material, wherein the neutron capture agent comprises a ⁶Li compound; and an organic or inorganic luminescent fluor distributed within the matrix material.
 2. The polymer composite of claim 1, wherein matrix material comprises at least one aromatic moiety selected from the group consisting of naphthylene, anthracene, fluorene, terphenyl, phenanthrene, pyridine, furan, and thiophene.
 3. The polymer composite of claim 1, wherein the matrix material comprises a polymer or copolymer selected from the group consisting of a polyester, a polyamide, a polyether, a polyimide, a polythioester, a polyarylvinyl, a vinylpolyether, a vinylpolyester, a vinylpolyamide, and a vinylpolythioester.
 4. The polymer composite of claim 1, wherein the matrix material comprises a polyester.
 5. The polymer composite of claim 4, wherein the polyester is selected from the group consisting of polyethylene naphthalate (PEN), polytrimethylene naphthalate (PTN), poly(9H-fluorene-9,9-dimethanol malonate), poly(9H-fluorene-9,9-di methanol terephthalate), and poly(4,4′-(9-fluorenylidene)-diphenol terephthalate).
 6. The polymer composite of claim 1, wherein the matrix material comprises a derivatized polyacrylic or polyalkylacrylic acid, wherein acid groups of the polyacrylic or polyalkylacrylic acid are derivatized to form ester, thioester or amide linked side chains, wherein the side chains comprise aromatic groups.
 7. The polymer composite of claim 1, wherein the neutron capture agent comprises ⁶LiF micro- or nanoparticles.
 8. The polymer composite of claim 1, wherein the organic or inorganic luminescent fluor is selected based on acceptor donor resonance and/or from the group consisting of 2,5-diphenyloxazole (PPO), 1,4-bis-(5-phenyloxazol-2-yl) (POPOP), anthracene, 9,9,9′,9′,9″,9″-hexakis(octyl)-2,7′,2′,7″-trifluorene, n-terphenyl, 2-biphenyl-5-phenyl-1,3-oxazole, 2-biphenyl-5(α-naphthyl)-1,3-oxazole, 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole, 2-(4′-tert-butylphenyl)-5-(4″-biphenylyl)-1,3,4-oxadiazole, n-bis-(o-methylstyryl)-benzene 1,4-di-(5-phenyl-2-oxazolyl)-benzene, conjugated polymeric and oligomeric dyes, metal organic framework dyes, quantum dots two-photon absorber semiconductor fluors and mixtures thereof.
 9. The polymer composite of claim 1, wherein the composite has a ratio of matrix material to neutron capture agent of between about 3:1 by weight and about 1:2 by weight.
 10. The polymer composite of claim 1, wherein the composite comprises about 5% or less by weight of the organic or inorganic luminescent fluor.
 11. The polymer composite of claim 1, wherein the composite comprises ⁶Li salicylate or ⁶LiF as a neutron capture agent and poly(2-vinylnaphthalene) (P2VN) as a matrix material.
 12. The polymer composite of claim 1, wherein the composite comprises ⁶LiF as a neutron capture agent and PEN as a matrix material.
 13. A film comprising a polymer composite of claim
 1. 14. The film of claim 13, wherein the film has a thickness of about 500 microns or less.
 15. The film of claim 13, wherein the film is a biaxially or uniaxially stretched film.
 16. The film of claim 13, wherein the film is thermally annealed.
 17. The film of claim 13, wherein the matrix material comprises PEN, the neutron capture agent comprises ⁶LiF micro- or nanoparticles and the film is a stretched and/or thermally annealed film.
 18. The film of claim 13, wherein the film has a neutron count rate per mg of ⁶Li of between about 4 and about 12 counts per second (cps).
 19. An apparatus for detecting neutron radiation, wherein the apparatus comprises a polymer composite of claim 1 and a photon detector.
 20. A method for detecting neutron radiation, wherein the method comprises: providing a polymer composite of claim 1; disposing the polymer composite in the path of a beam of radiation, wherein the matrix and the luminescent fluor of the polymer composite emits light when the composite absorbs said radiation; and detecting neutron radiation by detecting the light emitted by the composite, wherein the detecting discriminates between neutron and gamma radiation.
 21. A method of making a film or molded coupon comprising a polymer composite of claim 1, wherein the method comprises: providing micro- or nanoparticles of the neutron capture agent; mixing the micro- or nanoparticles with the matrix material and the luminescent fluor to form a mixture; and pressing and heating the mixture to form the film or molded coupon.
 22. The method of claim 21, further comprising stretching In some embodiments, the fibers have an average diameter between about 5 and/or thermally annealing the film.
 23. A method of making a film comprising a polymer composite of claim 1, wherein the method comprises solution casting a solution comprising the matrix material, the neutron capture agent, and the luminescent fluor.
 24. A fiber comprising a polymer composite of claim
 1. 25. The fiber of claim 24, wherein the fiber is prepared from a polymer composite comprising ⁶Li salicylate or ⁶LiF as the neutron capture agent and polystyrene (PS) or a blend of poly(2-vinylnapthalene) (P2VN) and polystyrene (PS) as the matrix material.
 26. A fiber mat comprising a fiber of claim
 24. 